You install the app.
Register with them how you want to pay.
Cash to the driver or credit card,or through PayPal.
When you need a taxi select your destination.will show the price and availabilty.
Confirm, then you can message driver.they seem to have discontinued being able to phone him.
You then see where the uber is on your app.
When arrived at destination.either pay the cash or confirm with him that the job is finished and paid with your nominated card.
There is now an option to give the driver a tip if you use cc.
I have used uber frequently for nearly three years in various mexican cities, never had a problem, apart from Guadalajara..rude ,wont take you to destination although they accepted it. Ask for more money than is quoted .etc etc.
If you dont use the app, they arent uber.simple.
Any rogues will probably not have any insurance cover either.