The best introduction I have found is from the Enco catalog. Fortunately you can view the catalog online. The introduction covers materials, types, number of flutes (including the trade offs), end cut type, shank type and surface treatments.

View the introduction at:

Note that this gives you page 123. Enco’s next release of the catalog may change the location of this introduction to another page. If you see this link is out of date please let me know the new page number.