Most cruises will include all the costs of food and onboard activities as part of the cost of the cruise. Travelers will be responsible for additional expenses such as alcohol, items purchased as ports and gifts or other services provided on the ship. Don't assume anything is covered by the cost of the cruise.
Research the ports of call or places that the ship will stop while on the cruise. If you know a bit about the various ports or areas you can understand where to go when you arrive and what you want to see. This information is often available on the ship as well as over the internet and in travel magazines.