One algorithm repeated, and the step where you have to trust a cube that looks wrecked.
By the end you will be able to
Get all four yellow corners facing upwards using a single algorithm
Hold the cube correctly between repetitions instead of guessing
Keep going when the cube looks worse than when you started
You have a yellow cross. The four corners around it are still showing yellow on their sides, and this step turns them all face up, so the whole top of the cube is yellow.
It takes one algorithm, done between one and three times. It is also the step that frightens people, so let us deal with that first.
The algorithm
RUR'URU2R'7
Seven moves, all on two faces. It twists three corners, leaves the fourth alone, and shuffles the top edges around without turning any of them over.
How to hold it
Everything depends on holding the cube right before each go. Count how many corners already have yellow on top — it will be none, one, or two, never three — and follow the matching rule.
Exactly one corner has yellow on top. Turn the top face until that corner sits at the front-left, then run the algorithm.
None, or two, have yellow on top. Turn the top face until the corner at the front-left has its yellow sticker on the left-hand face, then run the algorithm.
Then look again, count again, and re-hold. Three goes is the worst the cube can throw at you and most positions take two.
Two positions to try
No turns yet
One corner already yellow on top, at the front-left. This is the position the algorithm was built for, and one go finishes it.
No turns yet
No corner facing up. Turn the top until the front-left corner shows yellow on the left-hand face, then run it twice, re-holding in between.
What finished looks like
The entire top face is yellow. The sides are still a mess and that is expected — the corners are facing the right way but almost certainly standing in the wrong places, which is the next lesson. Two steps left.