Another good source of information is Wikipedia - just look up the part names. It will probably include links to more information than you care to read. You can get a lot of info, including an interesting history, just by looking up "computer".
A good source of general information about video cards is
How to Upgrade Video Card
It has information about identifying personal and system requirements, PCIe cards and slots, gaming and non-gaming cards, reviews, and installation instructions.
If you have a computer in the house, open it up and take a look, preferably with the system or mobo manual handy to identify parts.
It might be a long shot, but you could post an ad in Craigslist asking if anyone has an old computer they are done with that you could have to inspect and play with. It would be nice if it still worked, but even if it does not you could still learn all the parts and get practice dissassemblying and assemblying it.