Welcome. Be sure to check out eqemulator.org if you're interested in how stuff works both back- and front-end. There are tons of fantastic threads and utilities which can be applied to lots of different game engines - there's even an
ongoing discussion about completely redoing the game client in the Unity engine.
If you want to understand game mechanics the quickest, make an enchanter. Probably the most difficult class to learn, but also the most powerful - if you master that then you've pretty much mastered the game.