TL;DR Beginner's Guide to Mafia

This was all taken from RiceKirby's beginner's guide to mafia and list of terms from Miki Sayaka's original post in the Theme Guides thread. To have any idea on what is going on (if you're only watching games), at least read the What is Mafia? and Phases sections. Of course, if you choose to play, you will eventually need to have a basic understanding of the Power Roles and Additional Terms sections. As always, if anything is unclear or you would like further explanation, feel free to PM any MA on the server (get a list of them by typing /mas).

What is Mafia?
Mafia is a game that puts an Informed Minority (Mafia, seen as the bad guys) against an Uninformed Majority (Village, seen as the good guys). Each player is assigned a role when the game starts, and must work in accordance to help their team win. Mafia members (usually) know their teammates and can kill other players, but have less players. Village players don't know who's an ally or an enemy, but have more players. The objective of the game is to remove all players from the opposing factions. For any mafia faction (assuming all other mafia factions are eliminated), they only need to control at least 50% of the vote to win. The exception to this is VCLR (village can't lose roles; as long as at least one of these roles is still in the game, the village has a chance to win...even if the mafia controls at least 50% of the vote), roles that have the ability to 1v1 mafia roles. While the mafia can kill during the night, everyone can vote for a player they want to lynch during the day.

Phases
Each turn in a game of Mafia is divided into 3 Phases: Night, Standby and Voting Phases. Each phase is around 30 seconds long.
Night Phase (TL;DR where most of the actions are made) - Players with night abilities can choose to use their actions on another player during this phase, and the action will be executed once the night is over. Actions used during this phase are private; other players will not know who used which action. However, there is a chance that spies could receive hax on certain commands.
Standby Phase (TL;DR check what happened during the night) - This phase begins with the night's results being revealed. Players can check the deaths, inspections, and other information, and then discuss who could be the Mafia based on that. A few actions are available during this phase. Different from the night phase, actions used during the Standby are executed as soon as the command is typed. A daykill will remove a player from the game (and everyone will see this). An expose will publicly reveal another player's role or side to all players.
Voting Phase (TL;DR lynch a player) - During this phase, each player can vote for 1 person that they want to lynch. The person that receives the most votes will be lynched and removed from the game. If 2 or more players tie with the highest number of votes, no one will be lynched.

Power Roles
There will be power roles among the village with certain abilities to help them receive information, defend allies, and slow down the mafia. Among them include the following (note that any role with an * is a VCLR):
Insp - Inspector. A role that can learn someone else's role by Inspecting them.
BG - Bodyguard. A role that can Protect another player during the Night to stop them from dying to a kill.
SG- Safeguard. A role that can Safeguard another player during the night to stop them from being poisoned. (This tends to additionally protect from every night command that doesn't kill, such as distract, inspect, stalk, watch, convert.)
PL - Distracter. A role that can Distract another player during the Night to stop them from using any Night Actions.
Spy - Can learn what happens during the Night, no special commands. See: Hax.
Vigi* - Vigilante. A role that can Kill during the Night, but is sided with the Village. (Some roles have a chance to evade or counter a certain number or all nightkills.)
Samurai* - A role that can Kill during the Day, and is often times exposed upon doing so, and is sided with the Village. (Some roles have a chance to evade or counter a certain number or all daykills.)
Mayor* - A role whose vote is counted as 2 or more during the Vote Phase.
Anti-Mayor - A role whose vote counts as a negative number during the Vote Phase.
Exposer - A role that can Expose during the Day, revealing their role to everyone.
Neighbor - A role that can visit someone during the Night, informing that person of the Neighbor's identity.
Stalker - A role that can Stalk during the Night, learning whom their target visited.
Watcher - A role that can Watch during the Night, learning by whom their target was visited.
Converter - A role that can change one person's role into another. (This can also mean that converted person will end up on another team.)
Bomb - Revenges whatever action is used on it. Most of these tend to be nightbombs (kills whoever killed it during the night), daybombs (kills whoever killed it during the day), or votebombs (kills at least one person that lynched it during the voting phase).
Similar to bomb, there are also roles that do the same things as bombs, but counter instead of revenging. This simply means only the attacker dies, but not the actual target.

Additional Terms
Villager/Townie - A role that has no powers, or very minimal powers. They are the stuffing of a theme, and usually at least 2 spawn.
Mafia/Scum - Usually, this just refers to anyone who isn't sided with the Village.
Miller - A role that thinks they are a Villager, but if someone Inspects or Exposes them, they appear to be Mafia, even though they are actually sided with the Village.
Mole - A role that is sided with the Mafia, but if someone Inspects or Exposes them, they appear to be sided with the Village.
Poisoner - A role that can Poison someone during the Night, causing that person to die at the end of a later night. (Most of these roles tend to be sided with the mafia, but if this role is sided with the village, it is a VCLR.)
Priority Killer - A role that can Kill faster than anyone else in the game, usually before BGs.
WW - Werewolf. Usually, WW refers to a role that kills any PLs that visit them, and is often a solo role.
Kuja - A role that is unparalleled in the Vote Phase, by having 100+ Votes and usually a significant Voteshield. Whoever they vote for is almost always guaranteed to be lynched.
GF - Godfather. Refers to a solo role which is significantly stronger than most other Mafia due to being alone. Often they can kill twice per night, have extra votes, bulletproof, or are also Moles.
PR - Power Role. This refers to some strong role on the Village, like Inspector, Bodyguard, Samurai, Distracter, Mayor, Vigilante, Exposer, Spy, etc.
Claim - To reveal your own role (privately to another player or publicly).
Counter - To contest someone else's claim by saying you are the actual role that they claimed.
Connect - To connect PRs is to inform them who the other PRs are. The idea is to make it so every unique role knows every other unique role.
Clean - Someone who has been cleaned has been ruled out as a mafia suspect, meaning they can be trusted with the Village.
Hax - Some roles have a chance of identifying other roles and/or actions during the Night. This is referred to as Hax.
Lead - To initiate a Vote on someone that others can follow.
Lynch - The process of eliminating someone during the Vote Phase.
Meatshield - Meatshielding is a strategy that Villagers sometimes use: the idea is to claim a Power Role in order to attract Mafia to kill them instead of said valuable Power Role. Often it is risky, because if the Power Role thinks you are Countering instead of Meatshielding, they may try to lynch you. It is also usually unnecessary if there is a BG in the game.
Rand - Random Vote. Can also refer to any uninformed action, such as rand-killing, rand-PLing, rand-BGing, etc.
Reduced Deaths - If the amount of Kills during the Night is lower than is normally expected, there are a fewer reason to speculate as the cause. Usually, it means the Distracter was on a Mafia Killer that Night.
Reveal - To publicly confirm (or claim with evidence) someone else's role.
Voice - Someone who reveals information on behalf of a Power Role so that the Power Role doesn't get exposed.
Bus - Short for "throwing your teammate under the bus". It's a strategy used a lot in simpler themes. In order to earn the trust of the Village, a Mafia player might lynch one of their teammates, appearing to be a Power Role, or just a lucky Villager, which means people will assume they are clean. BTW, always make sure you have your teammate's permission before doing this.
Soft Bus - Similar to the above, but usually the intent is not to actually lynch your teammate. You might soft bus by voting a teammate if the lynch is already determined by the majority of votes. Alternatively, it can be used by suggesting your partner for a lynch, even if you don't lead the vote.
1v1 - A "One versus One" Vote. Two Players vote each other, while no one else intervenes. The goal is to test for Mayors, Anti-Mayors, or Kujas.
Spam - Typing your Night command in repeatedly. Sometimes, Power Roles can hax each other, so spamming the same command increases your chances of finding a teammate. Not to be confused with the kind of Spam that will get you server kicked.
PL Stall - Repeatedly Distracting the same person in order to stop them from taking action.
Voteshield - A number that is automatically added to a role if it is voted for. An example is Vaporeon in EV. Vaporeon's Voteshield is 2, so if 3 people vote a Vaporeon, then 3+2=5 so Vaporeon receives 5 votes.
Lylo (Lynch or lose): When the village needs to vote someone off or else they lose. This usually tends to be when there is one more person sided with the village than the mafia (assuming there is only one mafia faction present). Example: 2 village vs 1 mafia, 3 village vs 2 mafia
Mylo (Mislynch and lose): If the village lynches someone on their team instead of the mafia, they lose. This usually tends to be when there are two more people sided with the village than the mafia (assuming there is only one mafia faction present). This is also where you will often see NV@4 (no vote at 4) and NV@6 (no vote at 6) in the chat.  Do note that these won't apply to every theme. Example: 3 village vs 1 mafia, 4 village vs 2 mafia