You need a visa if you have a criminal record or have commited 'crimes of moral turpitude' (their words) otherwise you enter on the visa waiver programme.
How strange that you just think of this 2 weeks before sailing and hope you don't need a visa as it takes around 3 months to get one, by which time you would have missed the boat.
Janet, my friend, A of N, has sometimes got a convoluted mind which most times is advantageous but on this occasion may not.
Provided that you are a lawful and unsentenced person you just fill out a green "Visa Waver" form which will be given to you on the aircraft and hand it in at immigration. Neil