These instructions use the Firefox browser. Firefox is easier to use because it has its own certificate management and it is easier to download and save the certificate and private key. If you use Safari the process is more complicated, because it uses the Mac OS X keychain and Safari is not well integrated with keychain for downloading certificates into it.
Browse to the Comodo Free Secure Email Certificate page. Note: Comodo also has a Windows product called "SecureEmail" which is not what you want -- you just want an email certificate.
Click on the "Free Download" button.
Enter you name, email address, and country. A confirmation email will be sent to the email address for the next step.
Leave the key size on "high grade".
Enter a good revocation password and keep it safe. You will want to revoke the certificate if your private key is compromised or lost, or if you want to cancel the certificate before it has expired. To revoke the certificate you will need this password.
Read the subscriber agreement.
Check the "I accept the terms of this subscriber agreement" checkbox.
Click on the "next" button.
Firefox will generate a private and public key pair. Firefox will then send the public key to Comodo so that they can create a certificate with it inside the certifiate.
The private key never leaves your computer. No one knows what it is except you, not even the certificate issuer.
You might or might not see this dialog when Firefox is generating the key pair.
A page that says your "application is successful" should appear.
Check your email to get the collection URL and password.
Go to the collection Web page using the link in the email.
Note: you must use the same Web browser that you used to generate the key-pair, because it will match the certificate with the generated private key that was stored in the browser when the key-pair was generated.
Enter your email address and the collection password from the email.
Click on the Submit & Continue button.
If you see the following message, then everything has worked properly. There is now a copy of the private key and the certificate inside Firefox.
You can view your certificate by going to Firefox Preferences→Advanced tab→Encryption tab, and selecting the View Certificates button.
Under the Your Certificates tab will be the certificate that was created. The Certificate Manager also manages the private keys, but you cannot see it through the user interface.
Note: the free Comodo email certificate only contains your email address and no other identifying information. Which is why the certificate name is so unfriendly.
The next step is to export the private key and certificates from Firefox and import them so that your email program can use them.
Return to the overview or go to the next step of exporting certificates and private key from Firefox.