Ua
The algorithm, how to recognise it and how to practise it without cheating.
Recommended algorithm
M2 U M U2 M' U M211 moves
Alternatives
R U' R U R U R U' R' U' R211 moves · R and U only
How to recognise it
One side has a full bar and the other three have headlights: hold the bar at the back. The front edge has the colour of the right side's headlights.
Its inverse is another case
Do the Ua algorithm backwards, M2 U' M U2 M' U' M2, and you are solving Ub.
That's why CubeDojo never scrambles Ua that way: it builds a random state with the case fixed, so you practise Ua and not Ub.
Practise Ua now
Random-state scrambles, a timer and spaced review. Free, on the web and on your phone.