Hello ukimot5,
Thank you for your question. You can add a domain in cPanel, which creates a new folder for storing the site files.
Also make sure the domain is pointed to our nameservers.
You are not required to register the domain with us, but in case you need to, here is our guide on registering a domain in AMP.
If you have any further questions, feel free to post them below.
Thank you,
-John-Paul