I learned those skills from basically going to websites which sell all of the components of the computer and looking over the prices of the different parts. It is quite simple once you know the basics.
http://www.anandtech.com is probably the best computer hardware-related web site I ever saw. Many reviews and tutorials and also a forum with about 90,000 people who will answer any specific questions pretty fast.
BTW, http://www.newegg.com has very good hardware prices and they usually ship it out the next morning after you order your stuff.