How does it look?
In the example to the right you see, how such a message is looking like for not authorised readers. It is a text-only message with encrypted information between the start and end tags for PGP.
How to use it?
From version 78 the popular open source email program Thunderbird includes Open PGP and S/MIME encryption technology. To use PGP encryption, you and your communication partner have to install both an encription program based on the standard PGP. PGP stands for 'pretty good privacy'. After installation you generate your personal key. How to use it: Step-by-step explanation.
Find here an overview over other software and providers supporting Open PGP.
The idea: public and private keys
Every user of PGP has a private and a public key.
The public key is used by another person, that wants you to send a message for encrypting.
The private key should be kept secret: It is used only by you to decript encrypted messages of another person to you.