dennis embregts

hey i already have a server but i want my friend to be able to turn on the server when he wants to while i don't have my pc on (where the server is running ''not 24/7'') and if i want to i can turn it on so all by all the question what do i have to do to let some one else get on my server from his computer with out my computer (so hosting him self) and still the same server over and over again thanks..