The machines resemble rather large vending machines and are operated by tapping a card reader with your preloaded card. You can place money on the card in $10 and $20 increments at the table next to the machines. You'll be ID'd at the table when buying the card, but once you have it you won't need to be ID'd going forward. There are people watching the machines so if you look like you're 12 expect to be questioned.
As you pour the money gradually ticks off your account like a reverse gas pump. Be warned, if you have a bad pour and get mostly head you won't get a second chance without putting more money on the card. While the machines are fun to use, once the novelty wears off you'll realize we have bartenders to do this job for a reason.