It's really simple to use GPG to encrypt and/or sign email you send through Gmail.
Generate your private key.
```bash
gpg --gen-key
```
Extract your public key, which you will send to people you need to communicate securely with.
```bash
gpg --armor --export [email protected] > my_public_pgp_key
```
Install [FireGPG](http://getfiregpg.org/) and restart the browser. Use GPG in Gmail.