Your curiosity is admirable. I don't mean to brush you off, but rather, to direct you to some useful information. This search on ebay, using the term "introduction to biology" produces a number of hits, some seem both helpful and cheap. Changing the search to "introductory biology" produces more hits. Good luck.
Thanks
http://www.biology-online.org/
Here is a good link to start learning biology and its free!!!