On most Carnival ships you will have decent connectivity in your stateroom. You will need to pay by the minute or buy a package. You will connect the same way you do at any hotel or other pay for Internet venue. You will select your package or "pay by the minute" when you connect and bring up your browser.
Just remember your password and to "logoff" when you are done.
I suggest buying a package of multiple minutes. It is less expensive than paying by the minute.