On shared hosting
cPanel has two options for additional domains: parked domains (aliases) and addon domains. Both of these options are set under domains. Parked domains let you add an additional domain to your control panel as an alias of your main domain. For instance, you may want to add both a.com and a .net domain but point them to the same website. You would add the extra domain as a parked domain.
Note that to avoid duplicate content penalties by search engines like Google, you should redirect one domain to the other. Most software automatically does this, but you can set this by clicking “Manage Redirection” after adding the parked domain.
Addon domains point additional domains to external folders. Your main domain runs from the public_html folder by default. Addon domains can run from folders such as public_html/newdomain or just newdomain.
If you have a large number of websites to run, if your sites are functionally independent, and if you can afford it, we strongly recommend using a reseller account to manage multiple websites as an alternative to addon domains. The big downside of cPanel addon domains is that each website runs under the same user on the server, meaning that all website files are accessible inside one account, so any security vulnerabilities found on one site could affect the others as well. Another reason is that all websites will be using that one account’s resources, whereas in separate accounts they will benefit from more resource abundance.