Another thing is to read tomshardware benchmarks of CPUs, GPUs, Motherboards, everything. Those contain a lot of info and gives a thorough picture of how things work. Theory.
The practical part is piecing together a PC but once you understand the theory behind all parts, it is easier to troubleshoot a PC.
Read reviews! Don't just skim thru the text and look at numbers, read everything.
Another way if you like to read books is to get a hold of 'Upgrading and repairing PCs'.http://www.quepublishing.com/store/upgrading-and-repairing-pcs-9780789750006
I read one of the older editions, it was part of a course curriculum. I only skipped the printer part, wasn't interesting. Lots of good info.