maybe it is a very easy question but i do not understand yet what is really the difference between a domain ( i know exactly what a domain is), but not an add on domain or a sub domain, are they just two difference names for the same thing, are they just different url to find on internet the same web site??

Thanks again for any information i really appreciate it

domain: domainname.com
subdomain: subdomainname.domainname.com
addon domain: addondomain.com points to addondomain.domainname.com (or domainname.com/addondomain)

http://www.cpanel.net/docs/cpanel/ should give you more insight into how things are setup (if you're using cPanel).

lol you beat me 2 it aaah

Thanks for the links, i have a better idea now about subdomains and add on domains..