Welcome to Cruise Reviews!
As noted by others, your cruise price includes all entertainment, all the food you want in the main dining room, buffets, and room service, plus at select areas on some ships (such as sushi on some Carnival ships, or their deli's, etc.). You do pay for specialty dining or premium desserts, coffees, and of course all bar orders which includes soda.
The ships try to leave one pool open overnight so they can clean and adjust the chemistry in the other pools. Sometimes conditions dictate that they close all pools at night so they can clean them up for the next day.
Cruising is the best vacation value, but you do need to understand that onboard charges make up a big part of the cruise line income. More and more, the cruise price is getting more basic and ala carte charges are increasing. Here is an example: we just returned from a 7-night cruise and although in a suite with lots of perks we still managed to spend almost $1200 on extra charges while on the ship. This was all bar service, photos, gift shop purchases, specialty dining, internet time, gratuities for the staff, and some shore excursions.