First, determine what metagame you want to learn, there are two big ones right now, VCG and Smogon, there are some minor metas out there but most of them are 99% similar to Smogon anyways. Smogon is probably the best to learn for your purposes, it doesn't have that many opaque or hard to understand bans or rules. The main ones, other than which tiers pokemon fall into, are:
Sleep Clause (only one pokemon may be put to sleep at a time)
OHKO Clause (OHKO moves, entirely based on random chance, are banned)
Evasion Clause (Double Team is banned, because it lacks effective (keyword) counters)
Species Clause (You may only use one pokemon of each type, so you can't have two dragonites on the same team)
Moody Clause (the ability Moody is banned for being completely random and incredibly gamebreaking)
Drizzle + Swift Swim (Pokemon with swift swim may not be on the same team as a pokemon with drizzle outside of Uber tier)
http://www.smogon.com/bw/pokemon/This resource has good sets for almost every pokemon. Keep in mind, the way Smogon tiers are set up creates lower tier metagames so you can use shittier pokemon in an environment without stuff like Ferrothorn or Salamence everywhere fucking them. When you make a team, you need to have an answer for every major threat in a tier on it. You'll have to do a lot of trial and error (taking a team on showdown ladder, getting whacked, you'll start notice a pattern of what your team is weak to) to round it out.
Hitmonchan is RU so you might want to learn that metagame, it's easier to compete in less popular metagames because less people play them, but also harder because the fewer opponents are usually more skilled. OU is full of retards who think Charizard is the strongest pokemon in addition to people running the typical Jirachi/Politoed/Dragonite/Scizor/Ferrothorn/Jellicent team.
