There are several HOWTOs available.
You may get the best overview about the GnuPG system by reading the mini HOWTO available in several formats:
GnuPG supports the use of smartcards. This HOWTO explains how to install and work with these cards.
This smartcard howto is also available in the source repository.
If you have problems exchanging messages with a PGP 5.x system, you should have a look at this PGP5-GnuPG HOWTO available in English only. Note that PGP 5 is heavily out of date and should not be used.
Once you get familiar with GnuPG's mechanisms, you surely wouldn't miss one of its funnest (and useful) aspects: to meet your Internet buddies and get your key signed by as many of them as possible.
But having to check tens or even hundreds of keys at a meeting may become quite frustrating. Here it is where this HOWTO by V. Alex Brennen comes in handy. It is a guide to understanding and organizing a PGP keysigning party. Keysigning parties help build and strengthen the web of trust which serves to make the use of GnuPG more secure.
This HOWTO is available:
de · en · es · it · ru · si · zh-TW.big5 · zh-TW.euc-tw )
Firstly, because everyone should be using encryption and signatures in their email. Secondly, because there are absolutely no reason for you not to be using PGP-compatible software. Thirdly, because documentation is mostly geared toward someone who is already familiar with PGP. Fourtly, because we like to promote both GnuPG and Mutt as free software project, for use in everyday communications. Lastly, because Justin R. Miller likes writing tutorials.
For all these reasons, you can find below a link to Justin's HOWTO on how to send and receive cryptographically signed and/or encrypted email with GnuPG and the Mutt mail reader.
This HOWTO is available: