Where to start building a gaming rig? 350-400$ price range.

Hey guys, Let me start out by saying I'm not tech savvy at all, I'm also really, really poor.

I wan't to start building a rig for gaming (not anything hardcore, just low-mid settings.) but I have absolutely no idea where to start, I looked at the "falcon guide" but when I looked at it, the 300-400$ ranges looked so low-end, that It wouldn't even be worth the time. I can't spare more than 350-400$, hell, I likely won't even be able to buy a monitor, I'll have to borrow one. Fortunately I have a low-end keyboard and mouse laying around somewhere.

My situation is dire, please help.

Thank you in advance.