Encrypting your email communication is something that has been a complicated process to setup. Here's a video produced by Justus Ranvier that offers a step-by-step guide on configuring and using Thunderbird for email encryption.
To help out, here are some links to the software discussed by the video above:
Thunderbird Email Client: https://www.mozilla.org/en-US/thunderbird/
Enigmail Plugin for Thunderbird: https://addons.mozilla.org/en-us/thunderbird/addon/enigmail/
GPG for Windows: http://gpg4win.org/
GPG for OSX: https://gpgtools.org/