alright so this will basically introduce you to a LOT of major OU team types and it'll also give you some glimpses of how mons interact at the metagame scale. feel free to ask about literally anything i mention here. i basically want to see what kinds of teams you're interested in and what you want to build/know more about. if you see a team that strikes you as pretty cool, steal it and take it for a spin on ladder, see how it plays! (there's no stigma about stealing teams that have been RMTed)

probably the dominant team in OU is rain offense. politoed+maybe a defensive core (usually something involving tentacruel, ferrothorn, or jirachi) form the backbone of the team, and the idea is, generally speaking, to spam water moves/thunder/hurricane until you win. there are also niche abusers like toxicroak, that don't function on water/thunder/hurric spam, but in general spamming hydro pump is the way it works. defensive parts of the team will usually help set hazards and help your offensive mons get into play safely.
a lot of the RMTs for rain offense are from the tornadus-T era (torn-T was REALLY good so it was banned), such as http://www.smogon.com/forums/showthread.php?t=3477518.

on the opposite hand of rain offense, we have rain stall. this was bigger in BW1 than it is now. the idea is to abuse the great bulk of things like tentacruel and ferrothorn, who pair naturally with rain, and make a really really bulky team. chansey was also common on these teams - chansey's main weakness is residual damage since it has no leftovers, and rain prevents it from eating sand damage. teams like this are harder in BW2 - all forms of stall are harder than they were before, because the metagame's gotten more offensive. http://www.smogon.com/forums/showthread.php?t=3478627 is an example of a fairly stallish rain team, but even then only 4 mons are completely defensive in nature.

"sand" is probably the next category. this is REAALLLY broad so it's hard to be specific, and there are a lot of different ways "sand" can play. we tend to call it sand balance but it can lean towards stall or offense depending on the team. sand is a very flexible weather type because, by virtue of negating rain and sun, it brings a lot of things into the fray that would be at a disadvantage under those weathers. that's why there are SO many different types of sand team. in fact, sand doesn't often contribute a lot to the team, besides negating opposing weather and dealing some residual damage. because this category is so broad, it's hard to describe in detail, so i'm gonna show you some examples. feel free to skip ahead if you want to read these later.
http://www.smogon.com/forums/showthread.php?t=3480558 is an example of a fairly balanced sand team built around a fairly common "weatherless" threat, salamence. http://www.smogon.com/forums/showthread.php?t=3480557 is similar. you will see some recurring elements between them. for example, latias is popular on sand because its natural bulk makes it good against rain teams and sun teams alike, so it's a common fixture on sand. hippowdon seems to be the more popular sand starter these days - even on offensive sand - because bulky tyranitars just aren't that good right now.
http://www.smogon.com/forums/showthread.php?t=3479119 is a bit more oldschool in that it uses scarf tyranitar (a bit of a rare set in recent months). it also uses a very common combination for sand teams, keldeo+tyranitar. tyranitar removes bulky psychics and ghosts that typically wall keldeo (jellicent/celebi/latias) so that keldeo can clean up, and ofc keldeo is strong in rain as well so you can turn opposing weather against itself. another example of keld+tar is http://www.smogon.com/forums/showthread.php?t=3473737.
http://www.smogon.com/forums/showthread.php?t=3480364 is an example of a MUCH more stally sand team. you can see its defensive nature by the pokemon that dominate the team - jellicent, roserade, skarmory. as with all stall teams in this metagame, it's pretty hard to use six defensive pokemon and win the game. http://www.smogon.com/forums/showthread.php?t=3477612 is an older stall team (from the tornadus-T era). jellicent is common on these kinds of teams.

weatherless hyper offense - this is basically the only kind of team that runs no weather starters and is still considered competitive in OU. the term "hyper offense" refers to a team that uses many offensive pokemon. the pokemon are chosen to beat one another's counters (the things that wall them) and their checks (the things that revenge-kill them). they usually have one suicidal lead that lays down hazards at the start of the game to establish a good position and weaken the opponent's team early - previously deoxys-D, but that was banned recently (because it was too good at being a suicide lead). they prevent the hazards from being cleared with "offensive pressure" - in other words, you threaten your opponent with a lot of damage, so they can't afford to be cute and make defensive plays. eventually you want to build the pressure to the point of overwhelming your opponent and breaking their team open, at which point something can sweep and end it.
http://www.smogon.com/forums/showthread.php?t=3479904 is an example of weatherless offense in the post-deoxysD metagame. ditto is a powerful revenge killer since, with the imposter ability, it automatically uses transform as it switches in, which lets it steal opponents' boosts. http://www.smogon.com/forums/showthread.php?t=3479571 is a similar team, using the same stealth-rock-garchomp lead.

sun offense is a type of team that's arguably rarer on ladder than sand. sun has one major advantage over rain - drizzle+swift swim is banned (was too strong!), but sun+chlorophyll is not. that means sun can abuse sweepers that are much faster than anything in OU. if sun wins the weather war, it can often crush its opponent because of this advantage. of course, ninetales is pretty bad, so you win some and you lose some. in addition, sun has the nasty trait of being easy to counter - that is, you only need one or two pokemon to be at an advantage against sun. things like terrakion, latias and heatran are very good in this regard, and sun has difficulty overcoming them. this means that if your opponent has those mons, your game will be much harder, requiring more guesses/prediction and more risk - in other words, sun is inconsistent.
a lot of sun teams look really generic because they all need the same components to win, generally (ninetales to start sun, dugtrio to kill heatran, venusaur to sweep). http://www.smogon.com/forums/showthread.php?t=3479543 is a bit of an unusual example - it's a result of a metagame trend that made cresselia p good in OU, so players started making more defensive sun teams to take advantage of the opportunity.

phew sorry about the long read. that's probably about it. i focused on RMTs from players that are well known, but if you take a look at the RMT forum, you can find examples (of varying quality) of everything i listed. that might take a while though. this is basically just some more information for you to think about, so you can decide on what you want to build, and what you want to hear about next.