Encryption is when you change data with a special encoding process so that the data becomes unrecognizable (it's encrypted). You can then apply a special decoding process and you will get the original data back. By keeping the decoding process a secret, nobody else can recover the original data from the encrypted data.
You can use Mailvelope, a browser add-on in Chrome, Edge and Firefox, that securely encrypts your emails with PGP using Disroot webmail. Check this [howto](https://mailvelope.com/en/help).
