So Im not really good at the game so I was wondering, why does no marker show up on my map when I set a quest to be active when it should? And the quest Im trying to do right now involves finding the revered mother so that Sten will get released, so where is she?

She's in the  back of the chantry, once you enter the area it'll point you to her. This game REALLY doesn't really hold your hand and lead you around, best bet is to read the quest text in your log, it usually tells you where to go. 
 
Sometimes though, you're on your own and you just have to find shit, searching for people and objects is part of the game.

I kinda agree, I wish when you picked a quest it told you at lest a general area to look. But o well it is a pretty hard core RPG after all.