Step 1 - Log in to cPanel (click here for a guide) and click on the Aliases icon
Note: If you want to create a different website for this domain, use the Addon Domains feature instead (click here for a guide).
Step 2 - (1) type in the domain name then (2) click Add Domain
The domain will now redirect to the primary cPanel account. If you want to redirect the domain to a different website, click here for a guide on using the cPanel redirect tool.
Step 3 - To create an email account now, first click on the Home button in the top left to go back cPanel
Now click on the Email Accounts icon
Now when adding an email account, you will can click on the Domain menu and select the Aliase or Addon domain to use.