Secure Gmail encrypts and decrypts emails you send in Gmail. This happens all on your machine, and the unencrypted text never reaches Google servers. This is useful if you don't want anyone but the intended recipient to ever read your email (i.e. companies, governments, etc.)
Now refresh your Gmail Click on the lock icon next to the compose button.
Compose your email and send
Enter a password; your recipient will need to enter the same password.
To decrypt the email, your recipient will also need the Secure Gmail extension installed, as well as the password.