The Yellow Face
In this step we will get all the pieces in the top layer with their yellow panel on the top face. We are then set up to complete the cube in the final step.
This is done in two stages, first the yellow cross, then the yellow corners.
The cube will be in one of three states:
You will never have just a single yellow edge panel on the yellow face. If you end up in this scenario someone has twisted a piece on your cube and it is in an unsolvable state.
Thankfully, creating the cross involves one algorithm which is just repeated until successful.
If you have 2 adjacent yellow panels this is ideal and allows you to create the yellow cross with a single iteration of the algorithm. Start by rotating the top face so the two yellow panels are oriented as below.
You'll notice that the second 3 moves in the algorithm are the opposite of the first 3 but in a different order. Realising this can make it easier to remember.
If you have 3 yellow panels in a row like below then align the yellow panels horizontally like below, then apply the same algorithm to create the scenario above. Then repeat and you're done.
If you have no yellow panels on the top face then apply the algorithm once which will create a line of yellow panels, then align horizontally and repeat the algorithm to create a yellow L, then repeat again to create the cross.
Solving the yellow corners is also a matter of applying a single algorithm repeatedly until you get the desired result. Between each iteration of the algorithm you will need to rotate the top layer to align it correctly.
If you have the layout as below then a single iteration of the algorithm will solve the yellow layer. (note the orientation of the three yellow panels which are not on the top face.)
Remembering this algorithm becomes easier when you see it as a pattern of flipping back and forth between U and alternating R and R' moves.
For all other states just keep repeating the algorithm and rotating the top face until you create the layout above. Here are some tips to help you achieve that:
The two algorithms used in this step use the F, U and R moves. With practice you can perform combinations of these moves rather quickly. Spending some time practicing to get these algorithms smooth and fast will really help to reduce your cube solving time.