It's like a car rental service, except you can rent it by the hour. You pretty much go online, see when it's available, and make a reservation for a particular car for however long you want. You use your Zipcard to unlock the car at your reserved time, and the car keys are inside. There's a gas card for gas so you don't have to pay for that, and a lot of their cars are hybrids, at least at my school. When you're done using it, you return it to its assigned spot, and "check out" by locking the doors with your card. That's pretty much it.