Hi, Catherine! There are several ticket options to choose from when visiting Walt Disney World. Check
HERE for the different ticket options and pricing. You will notice that the more days of tickets you purchase, the "per day" ticket price goes down. Adding on the park hopper or no expiration will add to the cost of your ticket.
If you are staying off property, or are booking a "room only" reservation, you can get your tickets at the link above or you can purchase them at the gate or at any guest services or at Disney Stores.
To get a slight discount on tickets, you can purchase tickets through AAA or on-line sites such as undercovertourist.com. Remember, if you want to add the Disney Dining plan, you need to be staying at a Disney Resort and have at least a one day park ticket on your room reservation, in which case you will not want to buy your tickets separately.