Comma Resource

Commas have a lot of uses in English, but this guide should hopefully help you with a few of the more common ones. I'm including a glossary of terms at the bottom. Items that are in this glossary are surrounded by double asterisks the first time (**like so**) they pop up in the text, because this is on fucking pastebin and I don't have any better formatting options. This primer assumes that the reader has some basic familiarity with English grammar, especially word categories (e.g., verb, noun, adjective, etc.), but this will be subject to change if more explanations are necessary.
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1.) With lists
Lists of three or more things joined by a **conjunction** require a comma in between each item. The last comma (the one directly before the conjunction) is known as the Oxford comma and is occasionally omitted, but because it's the standard in CoC (and most of America), you should use it. Hopefully this rule, at least, should be familiar to you.

Examples-
Go to the store and buy milk, bread, and eggs.
He walked to the store, bought a few things, but forgot the milk.
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2.) With compound sentences
A compound sentence is one which contains two or more independent **clauses** joined by a conjunction. In a compound sentence, a comma must be put before the conjunction. This rule often confuses people, as it can be unclear for some when it's clauses being linked or verbs being linked or when a clause is independent or not. It's anecdotal evidence, but I feel that these are some of the most commonly missed commas for most people, so I would recommend trying to familiarize yourself with this rule.

Examples-
✓ I went to the store, but they were out of milk
//Here we have two clauses, each with a subject ("I" and "they") and a predicate (identifiable through the verbs, "went" and "were") which are linked together by the conjunction "but." Thus, a comma is necessary here.
X *Go to the store, and buy me some milk.
//This comma is incorrect, as there is only one clause in this sentence. While there are two verbs, there is only one subject, so the conjunction must be linking the verbs.
✓ Items that are in this glossary are surrounded by double asterisks, because this is on fucking pastebin and I don't have any better formatting options.
//This is a good example for illustrating what an independent clause is. "This is on fucking pastebin" and "I don't have any better formatting options" are both full clauses with subjects and predicates, but because they're both objects of "because," they're both dependent clauses, and thus there should be no comma before the "and" linking them.
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3.) Introductory phrases
This is a catch-all category for the various **prepositional**, **participial**, and other **phrases** which may appear at the start of a sentence, before the subject. These usually require a comma inserted afterwards, but when very short (I've seen four words or less given as a metric), it can sometimes be omitted. This only really works if the phrase in question is closely related to what follows, and since you're never wrong if you do include it, I would recommend not omitting these unless you have a solid grasp on what you're doing.

Examples-
On his way to the store, he dropped his wallet.
Searching the ground nearby, he found it in a bush.
After he stood back up, he noticed that there was some cash missing from it.
Yes, I'm already tired of making these.
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4.) With quotations
When a quote is grammatically integrated into a sentence with a **dialogue tag**, it must be separated from the rest of the sentence by a comma. If the dialogue tag comes after the quote, the comma replaces the period which would usually go there, but not exclamation points, question marks, or ellipses. Commas should go to the left of the quotation mark, and see the note at the bottom for a short overview of why that is.

"Well fuck," the man said.
He asked a nearby lady, "Did you see anybody touch my wallet?"
"No," she replied, "I didn't."
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5.) With parentheticals
While "parenthetical" technically means "inside parentheses," it is used for anything in a sentence which breaks off from the main point or is construed as sufficiently separated from everything else to merit being set off by commas. That's all a bit vague, but these commas will probably feel intuitive/natural once you see them for what they are. If you want to make this kind of interjection stand out more, you can also use em dashes (—) instead of commas (but make sure to look up how to use those).

Examples-
He, although somewhat exasperated by this entire situation, decided to be polite and drop the matter.
The woman, her mouth twisting into a grin, snickered as the man walked away.
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6.) With direct address
When a character (or you, if you're talking to somebody) calls someone by name/title in a sentence, that name is set off by commas.

Examples-
I'm not sure where I was going with that little story thing, anon.
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//
The above examples constitute the most common comma usages, as well as the ones people most frequently make mistakes with. The following comma usages are a little more specific, so feel free to stop here for now if all that was overwhelming.
//
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7.) With focus shifts
When the focus of a sentence changes part-way through, a comma is optional. This is a tricky subject, as you have to know when not to separate things which shouldn't have a comma between them and people differ in which commas of this variety thew view as "correct" (I, for instance, don't like commas before a conjunction only linking two verbs, but that's a relatively common usage).

Examples-
I'll move on to normal examples, as I've run out of creativity already.
I like the above example, but hate this one.
//Use the above with caution.
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8.) With participial phrases
This could be considered more of a subset of the parenthetical usage case, but it's specific/common enough to warrant a bit of explanation. Participial phrases are often seen at the end of a sentence, far removed from the nouns they modify (like "removed" in this sentence, if you don't mind me getting ahead of myself). These need a comma in front of them unless they directly follow what they're modifying.

Examples-
The fact that I'm writing a new sentence here instead of lazily reusing that one from earlier is honestly surprising, brightening my day just a bit.
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9.) With appositives
An appositive is a secondary noun phrase which follows a primary one to give it additional clarification. The rule with these is that if the appositive is necessary for identifying the noun, it's used without commas, but if it's not, you have to put them on both sides.

Examples-
You, my favorite poster, always put a smile on my face.
My brother Dan is imaginary.
//This appositive doesn't need commas because it's necessary for identification.
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10.) Lists of unrelated adjectives
Lists of adjectives that are all modifying the same noun in the same way must be separated by commas. The way to test this if you can add an "and" in between the adjectives, they need a comma. Another test is whether you can reorder them, in which case you also need a comma.

Examples-
Thank god I don't have to come up with another shitty, autistic example.
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11.) With question tags
Use a comma when there's a question at the end of an otherwise declarative sentence.

Examples-
Guess I was wrong about that one, huh? Can't always get 'em all.
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12.) With negation
Use a comma to separate parts of a sentence contrasted with "not" or another negative.

Examples-
This is a mod, not vanilla.
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13.) With dates/addresses
If you're writing long form dates or addresses in a porn game, I'm going to assume you're autistic enough to not need my guidance.
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666.) Comma splices
I'll be upfront about the fact that I'm a little bit more strict about these than some others, so keep that in mind while reading this. A comma splice is when two independent clauses are joined with only a comma, resulting in a run-on (this is essentially case 1, except without a conjunction). I've been informed that this is properly termed "asyndeton" (which you should appreciate if you're a boring loser like me). While technically incorrect, they are sometimes used when the two clauses in question are particularly related/close together. A semicolon (;) would normally be used in situations like this, but they're pretty gay, so people don't like using them too often (and you should be very careful of using them too much, especially in informal writing like CoC)(you know who you are).
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Bonus round.) Apostrophes
I'm including this because I see people fuck it up constantly, especially native speakers. ONLY USE APOSTROPHES TO SHOW POSSESSION (and contractions, but that's not the problem here). They are never ever used for the plural suffix, and I've even seen people use them for third person singular present verbs (e.g., *run's). Don't do this; it makes my eyes bleed. I'll also talk about the possessive with nouns ending in "s" (e.g., "demoness") There is a lot of variance in how people handle these, but I'll recommend you always use the full "'s" suffix if it's pronounced in the word (e.g., "demoness's). Some people omit them from all words that end in the letter "s" (but not the sound [s], as both "cockatrice's" and "Alice's" are fine with everybody), and some only do this with proper nouns. It's most important to be consistent, so just make sure that you always do this the same way.
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Glossary
//If you are ESL, I might recommend that you search for these terms in your native language, but feel free to plow ahead too.

Phrase- This is the first item on the list because it's an important one that's not likely to be known by a decent percentage of people, and I'll be using it throughout. Simply put, a phrase is a group of words which form a unit. Any clump of words which can be moved around in a sentence or replaced entirely by something else (like a pronoun for noun phrases or the word "do" for verb phrases) can be considered a phrase (these two metrics are known as constituency tests, but that's a little bit outside of the scope of this overview).

Conjunction- I generally use this term to refer to coordinating conjunctions and not subordinating conjunctions, but for an explanation of the latter, please see "Clause" below. These are words which are used to connect words or phrases together. There aren't too many of these, so you'll often see them grouped into the classic "FANBOYS" list (for, and, nor, but, or, yet, so).

Clause- A clause is a subject joined with a predicate (both terms are explained below). Clauses can be either independent or dependent, depending on how they're integrated into a sentence. Independent clauses are those that stand on their own. If you can take a clause out of the sentence it's in (minus any coordinating conjunctions used to join it with other clauses) and it still works as a complete utterance, it's an independent clause (these may be a difficult test for non-native speakers, so be careful). Dependent clauses are those introduced by a subordinating conjunction like "because," "when," or "if." When taken on their own, these clauses are known as fragments (a fairly common grammatical error).

Subject- This term can be a little tricky to define, as it's actually used to mean a couple different closely related things, but generally speaking, it's the noun that's doing/being the verb. For example, the noun "term" in the first sentence of this entry.

Predicate- This term has the same issues as "subject" with regards to definition, but it's generally viewed as the part of the sentence which isn't the subject. That isn't very helpful, so I'll note that you generally find them in English by looking for a verb to go with the subject of the sentence. If any of the last three terms are at all confusing, I recommend looking them up, as others will have certainly done a better job than me explaining them.

Preposition- These are generally defined as words which show the relationship between a noun and something else in the sentence. The reason this is so vague is that they can both describe and modify a lot of different things, but there are only ~150 of them in English, and some of the more common ones (in, of, at, etc.) are words that you know very well.

Participles- Participles are adjectives formed from verbs, usually using the "-ing" or "-ed" suffixes. There are irregular verbs in English which can have different forms (e.g., hung, brought, thrown, etc.). Be careful not to confuse these with gerunds, which are nouns formed from verbs using "-ing" (e.g., "I enjoy shitposting").

Dialogue tag- These are used to grammatically integrate dialogue into a sentence. They generally involve a subject and a verb that can take a direct object (e.g., "He says"). It's not enough that the verb can take a direct object, you must also make sure that nothing is filling that slot, because the dialogue needs to be the object of the verb.
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A closing note on comma placement with regards to quotation marks: commas should always go to the left (like ,"), even if they aren't part of what's inside the quote. This is what's known as Typesetters' Quotation, and it is standard practice in America (and mostly what's used in CoC). Logical Quotation is used in many other parts of the world (and may in fact be the superior convention), but consistency is important, so you should use TQ.
Update- Fuck all of that. We're real rebels 'round these parts, so you can use LQ if you feel like making a difference.
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Anyways, I hope this helps with your Mensa applications and/or the babyfur NTR snuff-fuck scene you've always dreamed of. Godspeed.