One thing you need to know - shipboard internet can be very slow, or even non-functional at times. RCI doesn't have internet managers. You sign up yourself once aboard, and if there is a problem you have to hope the person on duty at the guest relations desk can help.
To use the wi-fi you need to first sign up for an account at the internet cafe using the ship's desktops. Once this is done you can use your laptop. There will be information sheets about the process available - probably one in your cabin when you arrive.