Gpg is the OpenPGP part of the GNU Privacy Guard (GnuPG). It is a tool to provide digital encryption and signing services  using  the  OpenPGP  standard.

To easily encrypt a file called mydocs use:

gpg -c mydocs

You’ll be propted twice for a password, after that a encrypted file called mydocs.gpg is created. You can send this file to your it’s destine and send the password using some secure way. In the other side to decrypt the file:

gpg mydocs.gpg

That’s a very simple use of this tool, you can do much more.