Step 4: Make a yellow cross on the top of the Rubik's Cube?
So far we have solved two bottom layers and only the yellow face is left. In this fourth stage of our Rubik's tutorial we want to form a yellow cross on the top of the cube. At this point it doesn't matter if the edge pieces don't match the color of the side center pieces. We will switch them in the fifth step.
There's a short algorithm we have to use: F R U R' U' F'.
Besides the solved position there are two other possible patterns: an "L" shape or a line as illustrated below. In case of the "L" shape you'll have to do the algorihm twice, forming the line in the first stage. See the picture below to understand how this algorighm changes the top layer of the Rubik's Cube. The orientation of the cube is important, so the "L" shape is twisted as illustrated and the line must be horizontal.
F R U R' U' F'
See the animation below to see how you have to hold the puzzle in your hands when you execute the algorithm. Press the play button!
There's another algorighm, very similar to the one presented above which is a shortcut and takes you from the "L" shape directly to the finished yellow cross:
F U R U' R' F'.
This is the inverse of the first permutation. Play the animation to see how this is working.