Not having much of an idea what's going on at first is sort of the point. Look at it this way: you came to in a dungeon - you have no idea how you get there or why you're there, you were experimented on by some weirdo and your head hurts. You get out of the dungeon and you're not at all where you last remembered seeing the sun. Oh, and your old friend Imoen has just been arrested for trying to help you. Pop quiz - what do you do? I'd start exploring. It won't be long before you starting figuring it out, little by little. Exploring to figure out what's going is the best (and main) part of the game - it's really non-linear, so you'd best get used to it.
As for Imoen - you got it. Those spells are scribed in her book but she doesn't have the slots (on the left-hand side of the page) to memorize them yet - too low level.