The first layer

The cross is done. Now the four white corners, which will finish the entire bottom layer. There is only one sequence to learn here, and you will use it over and over — including, in a slightly different guise, for the rest of your cubing life.

Find the corner, then the slot

Pick a white corner — one with white on it somewhere. Read its other two colours: say green and red. It belongs in the gap between the green centre and the red centre, on the bottom. That gap is its slot.

Hold the cube so that slot is at the front-right, on the bottom. Then turn the top face until the corner sits directly above the slot. Now the corner and its destination are lined up in the same column, and there are only three possibilities for how it is turned.

The sequence

With the corner in the top layer directly above its slot, do that sequence and look. If the corner is not in, do it again. Keep going. Within at most six repetitions the corner will drop into place with white on the bottom, every time.

When the corner is already in the bottom layer

If a white corner is stuck in a bottom slot but wrong — in the wrong slot, or in the right slot but twisted — hold that slot at the front-right and do the sequence once. That pops the corner up into the top layer, where you can deal with it normally.

1. Hold the offending slot at the front-right, on the bottom.
2. Run the sequence once to lift the corner out.
   RUR^'U^'
3. Turn the top face to line the corner up above the slot it actually belongs in, then repeat as normal.

What finished looks like

The whole bottom face is white, and each of the four sides shows a solid band of its own colour across the bottom row. Not a T any more — a complete row of three. If a side shows two of one colour and one of another, a corner is in the wrong slot; lift it out and place it properly.