what type of computer you want to build.
If you just want to play around with them on the cheap, check out yard sales and thrift shops for cheap monitors and computers. Take a LIVE DVD with a Linux distro, and a LIVE USB flashdrive around to boot it up and run a command to get an idea of the computer's age and capability.
inxi -v7
at a terminal screen will give you all you need to know. Don't buy junk, don't get older than dual core computers. Linux is free operating system and there's quite a few of them.
http://www.distrowatch.com
Playing around in the guts of a computer that's all new expensive parts will turn you into a gutless wonder fairly quickly for fear of an expensive mistake. Not so if recycling and renewing some older computers on the cheap just to have fun.
Hang out at tech forums, read what seems interesting, it's haphazard method, but more fun than most structured courses. For structure, check out library books, read some online books. Above all, have fun, let it just sink in, like osmosis, you'll be surprised how quickly you learn a lot.
Hey I am 24. I live in North Carolina and my heart has always been in computers. I work fast food and I can afford to buy a new part every check. I would be so grateful if someone could help me with decisions on the best cheapest site to buy parts from and also which ones for the type of computer I want to build. I also have questions about my education and what field I should go into. I am very passionate about software and programming. I would appreciate anyone who would help me out.

Chowhound
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GameSpot
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TechRepublic