CSS, how does it work?

I suck at CSS and I dunno what to do. I know the syntax, selectors etc. and have no problem coming up with a design but I srsly cannot make it work. All I want is a basic two column layout with a top and bottom and can't figure this out for shit. Does anyone have a resource for actually learning this stuff well? I mean how to actually do an effective layout, not just "hurr durr, use property a to do whatever"

>>4
I did search for info, but all I find is how to use selectors and shit, not why my layout doesn't work.
I don't just want to copy layouts I want to be able to understand them and write them on my own.
But I'm not sure why you've given me that link. The site seems more centered on Photoshop than CSS.
>>5
Knowing who you're replying to would help.