Visually each domain will look seperate. You will be able to access
http://mymaindomain.com http://mycardomain.com http://myhousedomain.com
I know you said you don't want to know the internal, but it may help.
You main domain will hold the file for all additional domains (addon domains). They technically can be access
http://maindomain.com/seconddomain where "seconddomain" is a directory name YOU specify to just hold the files for the second website. When you type in
http://seconddomain.com, the server will automatically know to display files from the directory "seconddomain", and will treat that domain like it is the only domain on your account.
I hope that made sense... anyway just to elaborate.. In the browser address bar, each will be their own domain