The only question I can answer is that you can preregister. Go to the RCI website and under the heading "Before You Cruise" there is a button that says "Documents" or something like that. You need your last name, reservation number, date of sailing and ship name. Then just following the instructions and you will be preregistered. Print the page to bring with you.
As far as embarkation, I believe you will understand everything as it happens. If you are flying in early and staying at a hotel, you just take a cab to the port. Your documents may give more detailed information.
If you used RCI air and transfers, that will be as simple as looking for the RCI sign when you get off the plane.
It all falls into place ... you'll see. Try not to stress about it.