It's very easy to use. When you register in the app you have to enter your credit card, so the service will automatically charge you when you request a car and finish the journey. So, you don't have to worry about having cash with you or anything.
The app interface shows you exactly where the vehicle that is going to pick you up is, what model it is, and who the driver is. In addition, once you've finished the trip, not only will you receive the receipt on your device but you can also rate the experience.
Uber is a relatively useful service that allows you to travel from one side of the city to another quite cheaply. The best thing about it is that the payments occur automatically, without having to lift a single finger.
Requires Android 4.0.3 or later.