Mr. Taylor,
You need to know at the outset that if you intend to engrave guns that are not your own you will need to have a federal firearms license.
That said, to learn about the tools, styles, and terminology of hand engraving click on the link below my signature to view the engraving glossary.
The best instructional manual for beginners was just published and is sold on this site. The title is
Engraving Historic Firearms by John Schippers. Don't let the title throw you off. The instruction applies to anyone who wants to engrave firearms or knives. Here is the link:
http://www.airgraver.com/Engraving-H...-Schippers.htm
RB