I finally took my first uber ride today. Since it was Sunday, I could risk a metered taxi in Lagos and since I hadn't left my house in a week, I could risk taking a taxi at all (but that's a story for another day)
It's pretty easy. You download the app, put in your card details and you're all set. (All uber rides get charged to your card)
The app finds your location, you put in your destination and a driver will be sent to you. You can track his movement on the app and the app updates with estimated arrival time.
The taxi is metered AND the prices are high calculated based on time and distance, so be careful if you want to jump in it on a random regular day.
I would definitely use it again on a Sunday. On a weekday? Easy taxi.