I got a job offer letter from the cruise ship...

, please be noted that if you wish to go for work, then you have to receive a job offer, bu which you can apply for a temporary work visa at the United States embassy. You have to get an approved I-129 and a broad-based work form from the administration US Citizenship and Immigration Services. The document sould be submitted by your employer at a time before the expected employment's starting date, which shall be within no more than six months, and you can not enter the United States of America up to ten days before your initial employment starting date as mentioned in your I-797 form or in the offer letter.
If you want to travel to the US to search for work on your own or wish to go for tourism or a visit, you can get a tourist visa and / or in general to obtain any type of visa, you have to fill out the visa application form, which you can get from the US Consulate's website  after creating an account and booking the interview datee. Then, you will pay for the visa fees at  Service Center and you MUST come in person to the consulate in order to attend your interview. Bring your valid passport at least for six months after the expected period of residence in the United States
As in regards of the period of the visa validity, it shall be determined when you arrive at the airport terminal where the customs and border protection officer in the United States processes your entry and residence period in the country