It possess you to do naughty things.

Wut... when do I get that? o-o

15? 18? Something like that. Ziola gives the quest, I think.

Im fuckin stuck with my rogue
I cant find any quests and I dont understand how to use the available quest thingie...

the available quest button is at the bottom left of the quest window. it's a list of quests that are available to you and where to get them from.

There are some quests that are shown in the available quests window that I can't seem to pick up. :/

I already know that. But there is like 893247 categories and quests for different lvls? How do I know which ones are my lvl and which category should I be looking under.

Pick red, yellow/orange, light blue... and anything that gives a decent amount of exp. Really doesn't matter which one you pick up.