Once you purchase your Walt Disney World (Florida) tickets, you will have the option to create your Disney Account. Doing so will allow you to skip lines with your Fast Pass (one per ticket purchased).
To begin, start by creating your Disney Account by going directly to: https://disneyworld.disney.go.com/registration/ or logging into an existing Disney Account by going directly to: https://disneyworld.disney.go.com/login/
Register your full name, email, physical address, and date of birth, including the names of those you'd like on your reservations.
Then, link the Disney World confirmation number found in your Vacation Planner Itinerary PDF. (*Note, the confirmation number is case sensitive. Select My Disney Experience > My Reservations and Tickets > Tickets and Passes > Link Tickets).