Well - we could just point you to the faq - but basically there are two games being played - both based on the same random combat generator.
The first, YB, is a tournament game where kung-fu fighters (and some other odds and ends) compete and win or lose rank as they win and lose fights.
The second, YBA, is an offshoot of YB and in YBA adventurers wonder around, beat things up and collect experience and loot.
Both are simple, mindless and slightly addictive games.
Some of the other threads here deal with IC roleplaying (mostly for YB) and with the new rules we are about to release for YB - likely on Feb. 4th.