I've been reading lately from this website, a lot of Gun basics.
It is simple and straightforward information and nothing fancy, if you have the patience to read.
I'm unsure if the site has been discussed here earlier but fell no harm in posting. Here it goes:
http://www.recguns.com/Sources/topOutline.html
For beginners like me, the "I. Introduction" and "III. Firearm Information by Type" hyperlinks on the page would be most revealing.
Happy reading
Virendra