A Basic 5-Step Solution of Rubik's Cube
Step 3: Solve Middle Layer Edges
This is where things begin to get tricky. You don't want to mess up your progress so far in solving the top layer so we need a move sequence that allow edge pieces to move into the middle layer while leaving the top layer untouched. In the video we show you how to use the two move sequences listed below the video.
To find out more about communtators see Lecture 13 of the course notes, or start with this video.