1. Login to the webmail program you prefer. You can get there by going to your-domain.com/webmail. You'll need to log in using a username (which is the full email address) and password.
2. Once you have logged into webmail, click on the webmail program of your choice.
3. Copy the URL in your address bar. It will look something like:
Note: You must replace your-domain.com with your actual domain name in the above examples.
4. Once you have the URL you'll be wanting to use, log in to your cPanel.
5. In cPanel, set up a subdomain called something like myemail.your-domain.com (you can do this by clicking on the "subdomains" icon in cPanel). Do NOT use mail.your-domain.com as these particular subdomains are already in use on the server and attempting to use them as subdomains can result in conflicts.
6. After you've set up the subdomain in your cPanel, set up a "redirect" for the subdomain (by clicking on the "subdomains" icon). You will need to set up the redirect so the subdomain goes to the URL of the webmail program of your choice.