MMORPGs
To make an MMORPG one must absolutely learn about the HTTP protocol! Unless you want to make one of those MMORPG based on some kind of website they run on, and if you want to step up your game, this is necessary.
You will have to learn the ins and outs of this protcol which allows you to send certain requests to a server and back. You will have to instantly update information, things, etc., and share it between many users.
Have fun! Haha...
And don't forget the art you're going to have to draw. You may, for this, watch a few guides on making MMORPGs, try some graphic design, and even... find books.