The slot machines on Princess Cruises are "activated" by using your Cruise Card (Room Key) and you must setup a pin # when you first sit down to play. I have seen confusion on whether to use cash or charge to your room and want to share what works for me.
There are no paper tickets or payouts - all money is stored on your Cruise Card. You may "charge your room" for any amount to play with or insert cash into the machine. Either way when you "cash out" your winnings from that machine, the money goes to your Cruise Card (NOT BACK TO YOUR CREDIT CARD OR BILL FOR ROOM). You can then move to another machine and download an amount from the Cruise Card to play with or take your cruise card to the cage cashier and take cash from the Cruise Card. Show your card, input the pin you setup and they will hand you cash.
That said, I have found it is simpler to start with the amount of cash I am comfortable "losing" for the cruise and work up or down with that. E.g. Insert a hundred dollar bill and keep uploading and downloading play money. Should I win a large amount, I may go to the cage and take a partial amount of cash off - leaving the initial $100 on the card to continue to play. When you charge to the room, be aware that the credit or debit card you have on file will be debited. (TIP: Rather than atm cash, download cash to your Cruise Card and take to the cage and you will not be charged any atm fees.)
It is really easy to keep charging increments of money to the room and all of a sudden realize you have spent more than you want to. Therefore the cash concept is a good one.
You accumulate points as you play and on some cruises, drink credits. You pay for drinks in the casinos unlike most casinos that pump you with free drinks! However, when you have earned points and drink credits, they will use those if you ask in lieu of payment. If you have a lot of points (over 3000), they will probably reward you with free cruises or casino cash for your next cruise! Be sure to take off or play any remaining credit you have on your cruise card on the last night because once you leave the ship, it's gone and does not go toward your room bill!!!