It looks like you're new here. If you want to get involved, click one of these buttons!
here is a very simplified explanatory website: http://l2info.arktic.net/
it seems to be not only concise, but also well organized. of course b/c of the complexity at this time of a 7 year old game, you will need to supplement it if you need more details. however, for quick, concise intros to get you started this is a good one.
"There are at least two kinds of games.
One could be called finite, the other infinite.
A finite game is played for the purpose of winning,
an infinite game for the purpose of continuing play."
Finite and Infinite Games, James Carse