http://o54hon2e2vj6c7m3aqqu6uyece65by3vgoxxhlqlsvkmacw6a7m7kiad.onion/en/help/how-encrypt-messages-asymmetric-encryption
If you are creating a key to be used when sending email, then it makes sense to use the information that corresponds with that email account. After you've supplied this information, you will need to enter a password to protect where your private key is stored on your computer.