You log into a workstation using your user name which is your first initial, last name, and cabin number (e.g. "gbush8030"). Your initial password is the six digits of your date of birth. You will immediately be asked to change your password.
You will be asked whether you want to purchase the unlimited package or pay by the minute. Either way, your charges will be charged to your stateroom account.
Although some Internet Café managers may tell you differently, yes, your entire family may share a single login. However, only one person at a time will be able to use that login, even if your teen is using it in Common Grounds.
BTW, it's "KTTW" for "Key to the World".