Just fucking do it. Set goals: figure out what you need to do to get your GED (or whatever you crazy Canadians call it). Make a list of the steps you need to follow in order to get it, and cross off each step after you've completed it.
Get yourself into a community college... don't even think about trying for a major yet, just take one class in whatever subject you think might interest you. If you're as smart as you say you are, your brain will probably latch on to the first real class you take, and you'll find yourself a lot more motivated. (I know that's what happened to me: a year ago, I was going to a community college because I didn't know what else to do, and now I'm accepted into a very good four year school, all because I decided I actually liked learning.) Do some research into which professors are the best, and pick one everyone likes.
And in your free time, just get out of the house more. Take walks, go to cafes and watch people. Get into AA, if your drinking bothers you so much and you can't stop.
But mostly, just get up and do SOMETHING.