For onsite guests, the magic band is the normal ticket. It is also your room key and your link to you fast passes.
In the old days, you would buy a ticket and, upon checking into your hotel, receive a room key and upon arrival at the parks, insert your ticket into the FP machine to get your paper fast passes.
Then, one day, Disney decided to make your room key and park ticket all one thing for guests staying onsite and booking a ticket/;room package (those who bought separately still had to cards in their pocket).
Now, Disney has put everything all in one place and you access it through your magic Band.
If you have a credit card set up for room charging privileges, you can use your MB to charge everything in addition to everything mentioned above.
