Basically, what's going to happen is cPanel will create an almost independant hosting account for this new domain name of yours.
So I have "example.com" and I'm making "example2.com" my addon.
If I put "example2.com" into my browser, it will pull it up and work mostly independant from our first domain/account, "example.com".
I will make an addon domain for my account and show you. Give me 1 hour.
Ok. So now I've done it.
I own phirefast.net. I have made "calmacc.com" an addon domain of phirefast.net.
Now I will upload whatever files I want to appear at calmacc.com, to "calmacc.phirefast.net," with the following login information:
FTP Site: phirefast.net
FTP User: calmacc@phirefast.net
FTP Password: woops - can't tell you that one!
http://phirefast.nethttp://calmacc.comhttp://calmacc.phirefast.netYou see now?