It's Jonathan. Lol.
And I think Thomas has just about covered everything there. Do add the new domains, in cPanel you simply go to addon domains and create them there. This will create a new directory and a subdomain on your account as well as the domain itself.
For example say you had your main one as microsoft.com and another as google.com, you could create the directory called google and then the subdomain would be google.microsoft.com but you could also access it from google.com. That's just the way cPanel does it but from what you've said, that should be fine.
