Currently there is no extra charge.
You need to have your admission ticket re-issued on a card with an RFID chip, or have your ticket admissions transferred to an RFID bracelet (Magic Band). These actions are performed at a ticket booth or in some cases at a Disney's resort's front desk.
Go to a new Fastpass kiosk; they're located conveniently throughout the park. Press your RFID card or bracelet to the target (sensitive patch), then follow the instructions on the screen to choose the rides you "want to Fastpass (v.t.)". (Currently limited to three rides/shows with some combinations/repetitions of the most popular rides restricted.) You can choose what time you want to go to a particular ride, subject to available time slots.
At the appointed time or (in most cases) up to an hour afterwards, go to the ride just as you would have using a paper Fastpass. Press your RFID to the target (which is a small ball with a Mickey head on it) and it lights up green to admit you. (A CM is there to help you.)
If you have a Disney's resort room reservation and you have your tickets in hand (or with a resort package), then you can make Fastpass reservations in advance at your home computer or using a smart phone. Then you would be able to make changes but not make more Fastpass reservations at the kiosks in the park.
Regarding the RFID bracelet, you would buy one for each person, or use the ones you had from last time, or one for each person comes with a resort package or meal plan.
