where can I get an explaination of the

[Stoney]

different primers, i.e. small, large, pistol, rifle?

[Artful]

What kind of explaination are you looking for?
Diameters differ between large and small to fit the different size holes in the cases. (IE most calibers come with only one size pocket large or small)
Rifle vs Pistol - well Rifle have more mix for more flash - harder cup to handle higher pressure - basically one is designed for rifle use the other pistol. When you step up to magnum primers in either flavor they add more priming compound to give a hotter longer lasting flash to help ignite either in cold weather or more powder or both. Mil. spec always has a harder cup for use in semi-auto rifles to keep from getting slam fire.

You will find there are differences in using different makes primer.
http://www.accuratereloading.com/primer.html

there are some cases out there that come either large or small - I have a few .38 spl with large primer pockets instead of normal small primer pockets - so nothing is an absolute.

Is this what you needed?