You can find an article explaining in details how PGP works here - http://users.ece.cmu.edu/~adrian/630-f04/PGP-intro.html
The wiki for PGP is available here - http://en.wikipedia.org/wiki/Pretty_Good_Privacy
If you need information on how to setup PGP with your Email, here are some articles that will help you. Please note we do not recommend or suggest any one product over the other. These links are purely a place for you to start your research for a product that best suits your needs.
PGP Desktop Home: http://www.pgp.com/products/packages/desktop_pro/
Company: Symantec (USA)
Price: $99 USD / 91€
OS: Win 2000, XP, Vista & 7 - 32-bit and 64-bit for Vista and 7, others 32-bitOutlook: XP, 2003, 2007 - Express and others also supported (not a plugin)
Support: PGP/MIME, OpenPGP, S/MIME, X509 v3Algorithms: AES 256-bit, CAST, TripleDES, IDEA, Twofish
Notes: Difficult to use, not a plugin, but a proxy style encryption/decryption software the sits between the mail client and the server. Industry standard and one of the few with enterprise level support available.
Company: Gpg4win project
OS: Win 2000, XP, Vista & 7 - 32-bit version available (works under 64-bit)Outlook: 2003, 2007 (plugin type)
Support: PGP/MIME, OpenPGP, S/MIME, X509Algorithms: 3DES, CAST5, Blowfish, AES up to 256-bit, Twofish, Camellia up to 256-bit
Notes: Perhaps the most hacky and geeky. Has extensive documentation, but not perhaps the first recommendation for newcomers to encrypted mail.
cGeep Pro: http://www.cgeep.com/features.html
Company: SafeLogic (Germany)
OS: Win 2000, XP, Vista & 7 - 32-bit version available (works under 64-bit)Outlook: 2000, XP, 2003, 2007 & separate version for Outlook 2010 (both plugin type)
Support: OpenPGP Algorithms: Blowfish, AES 128/192256, CAST, 3DES, up to 4096-bit RSA keys
Notes: Perhaps the easiest interface for beginners to learn & use
OS: Works with Windows or Mac using Thunderbird as an Email client
Support: OpenPGP Algorithms: Blowfish, AES 128/192256, CAST, 3DES
Notes: This is the simplest install for beginners and advanced users alike - friendly interface. A screen by screen install instructions are available here https://www.wefightcensorship.org/article/sending-encrypted-emails-using-thunderbird-and-pgphtml.html
GPGMail V2.1: https://gpgtools.org/
OS: Mac using Mac Mail
Support: OpenPGP Algorithms: Blowfish, AES 128/192256, 3DES
Notes: The best solution for MAC users
If any errors are found regarding compatibility or OS support please let us know.