The ticket needs to be linked to your
MDE account. If you bought from the Walt Disney World Website, than it probably is already. If you got them from
Undercover Tourist or another discounter, then you'll need to link them in MDE.
The ticket then becomes the "key" to your MDE account.
Think of MDE is as a house. That house has rooms named ADR (dining reservations), Tickets, Resort Reservation details, Fast Pass Plus, Recreation Reservations, Tours, Etc.
The house has a lock on the only door. That door has a number. Your ticket (or Magic Band) is encoded with that number. Once the ticket/band unlocks the door, a computer terminal can access the information in your MDE "house" and grant you access to all the Disney fun you've reserved, or purchased.
Does that make sense?