OP: Back in the day (a couple decades ago), building your own used to be tough and you used to have to be "techy" and whatnot to do it. Nowadays, if you can read an instruction manual, are careful with parts (don't force anything that doesn't fit, handle things delicately, etc.), and are handy enough to put a piece of furniture together that comes in a kit, you can build a pc. There are tons of videos (youtube comes to mind) online that show it as well. I would start by watching some of those to get the feel for it first but building a pc really isn't the forbidden art it used to be anymore.
Take it slow, keep a machine handy to come here for help if you get stuck, and you can do it. You'll also feel really proud as YOU built it.
When did Best Buy sell you that piece of junk by the way? Can you still take it back for a refund?