Well right now we have a party playing once in a month but well honestly less.. Time flies..
Yes there are rules which define more or less what can be done and have hard hings are to make the gameplay move effortless forward, Some games have very advanced rules that more or less makes it a preferance that thoose playing have to know alot about the rules whereas some are simplier and more fluent like the DoD game which are pretty easy to start with. The games are in the end what you make them to be.
There are no leagues tat I know of since roleplaying basicly are about cooperation, but there are Official groups that hosts different types of gaming styles though.
If you want to start to take alook at Roleplaying as a Pen and pape way to play I suggest you chek out Dungeons & Dragons. Very basic and real good with the material you can find to it. Alots of worlds and good authors who you can be inspired of. Second find some friends that wants to try it out cause you should be at least three players to get the real fun to come..
Check out
www.wizards.com (again) cause there you can download alot of free material to have a check at it. Look up roleplaying than dungeons and dragons..