PGP, or Pretty Good Privacy, is a public key encryption system for email and files. GnuGP is a version of PGP designed to be an open source code version of PGP based on the OpenPGP standard.
There are two general methods to use PGP: encryption and digital signatures. For encryption you obtain a public key for the person you wish to send encrypted email to, and then encrypt the mail with that public key. Only the private key (which only the owner should have) will allow that message to be decrypted.
The other use of PGP is to digitally sign a message. In this case you sign the message with your private key. Anybody wishing to check the message may do so by verifying the signature using your public key. If the message has changed or was not really signed by you, the receiver will be able to verify this.
My older DSA key with key ID 0x01475C4F with fingerprint F112 681B 2678 B61B 7AC9 D69F 5D6A C005 0147 5C4F expired on 30 January 2019.
You can also download the text version from here: