They are wristbands that you can wear to:
Instead of using a regular Theme Park Ticket. Just simply tap your MagicBand, put your finger on the scanner, and enter!
Fastpass+ is like the old Fastpass, if you remember that. But instead of going to the attraction and getting a time, you can book them ahead of time. 60 days ahead for Resort Guests, 30 days ahead for everyone else. You get 3 Fastpasses per day, and can book additional Fastpasses for the day after you have used those 3 at the park.
PhotoPass is Disney's professional pictures, you can get them taken at various places around the park and at most character meet and greets.
- Pay for merchandise and food (Only if staying at a Resort)
Resort guests and Passholders get their MagicBands for free.
If you are staying at a Resort, you can choose between Blue, Pink, Green, Orange, Yellow, Red, or Grey. They will be shipped to your house before you leave for your vacation.
If you are not staying at a Resort, you can simply use your Theme Park ticket to enter the park and use your Fastpass+, And they will give you a separate card for PhotoPass.
Or, you can purchase a MagicBand for $13. They also have Anna, Elsa, and Olaf MagicBands for sale at Hollywood Studios. Sometimes there are Limited Edition bands, but those of course, will vary.
They work by using RFID technology. All you have to do it tap the MagicBand on one of the RFID scanners to use it, Same way the current tickets work too.