To warm you up quickly:
for a primary domain name try something like   hopper.home  (or anything else that sort of looks like a domainname, but is not really one. 
lastname.home  lastname.iglo  lastname.snow
anything.home  anything.iglo anything.something
you get the drift...
these names are not proper domain names, when you hook your system to the net, and want it to be visible form the net (do you really want that??)  then you can simply change it to another domain name. 
I always make up a name for internal use, therefore there is less risks my box is visible on the net.
the sme box believes anything you tell it, as long as it is in the format
 something.somethingelse
but DO NOT use an existing (someone elses) domainname!
get better quick, read the manual, start experimenting, and you will see that all your questions have already been answered!
kees