It is very important that you read the documentation that comes with PGP before attempting to use the program. If you don't understand the basic principles behind public key cryptography, then you may very well jeopardize both your own and other people's security, and PGP will only give you a false sense of safety. This fact cannot be stressed enough! The links below should provide you with the information needed to avoid most pitfalls.

Books

Frequently Asked Questions (15)

History of PGP by Adam Back

How PGP works

Known bugs in PGP (4)

Overview of PGP

PGP 2.x (4)

PGP 5.0 (2)

PGP 5.5

PGP 6.0

PGP 6.5

PGP 7.0 (3)

PGP User's Guide (50)

Specifications and standards documents (5)

Why do you need PGP? by Phil Zimmermann (10)