Your documents will arrive anywhere from 2-4 weeks before your cruise (sooner if you booked your flights separate from the cruise line, later if you booked your air through the cruise line.) You will get a book of vouchers for each adult in the cabin, possibly a separate set for each child as well. Take them all with you, and make sure to pack them in your carryon bags, not
in your checked luggage! You will also be asked - if you haven't been already - to fill in passenger information before you sail, and it will save you time if you do this at least 2 1/2 weeks before your sail date. You can do it online at princess.com; you'll need your booking (confirmation) number and your name.
Among the things included in your documents will be your "ticket" for the cruise, a form to sign for your onboard account, and the cruise contract, which you would be wise to read, even though it's long. If you have booked transfers to/from the airport near the cruise port, you will find vouchers in there for those too.
Hae a wonderful time!! Relax and enjoy - that's what cruising is about.