I don't know much about WoW, but it seems like you should just abandon your previous experience and start with a clean slate.
At the fundamental level, there are a small handful of different roles. The two big ones are damage and healing, both of which are self-explanatory. In PvE, this is pretty much all you really need to roll through the game in most areas. The best professions for this are Warriors, Assassins, Dervishes, Necro's, and Ele's in the first half of the game. Mesmers and Monks can deal some damage, but usually aren't as good for damage as the previously mentioned professions.
Then, there is the support/utility role (which are somewhat the same things), and the shutdown role (which is rare in PvE). Ele's, Paragons, Ritualists, and Rangers generally play the former. Through things like snares or blind, interupts, party support healing/damage mitigation, or even a hybrid of damage and healing, they provide things that pure damage or healing can't do. Shutdown is basically just using your skills to prevent another from using their skills effectively. However, since usually it's hard to shutdown more than one or two foes, and mobs coms in anywhere from 3 to like 15, shutdown is pretty useless in general PvE (though some bosses can require shutdown).
So basically, you should try and pick what type of role you would like to play, and decide your profession and skillbar by that choice. For specific build suggestions, try PvXWiki.