When you book a stay onsite then usually you get to customise your free magic bands, or upgrade them to special ones, online. At the moment true is disabled, but it will come back in time for you. You have a certain time frame to do that and then they will post the bands to the lead name.
You also need to create a My Disney Experience (MDE) account. Everyone can be on the same account, or you can each have your own. Once your reservation and tickets are added to your MDE account, your magic band accesses all the information. Your magic band can be used to get into the parks, tap into FPs, open your room door and charge back to your room account if you want to.
To book fastpasses you must all have a ticket linked. And if you have separate MDE accounts, you can link them together as “family & friends” so one person can book all the fastpasses. Buy the tickets 60 days ahead to be able to book them for your trip.