Ah yes, welcome to the learning experience
The USB key is indeed an iLok. You need to go to iLok.com and create an account(its free) and then register the iLok to you account. The iLok MUST be plugged into the computer, whenever you want to run Pro Tools. As for having no CD/DVD drive, I suggest buying a USB optical drive(CD's and DVD's are not dead yet, and archiving to DVD-R is a good way to back up your sessions....you DO back up your sessions, don't you?)