Completing the 2nd Layer
In this step you have to place the four 2nd Layer edges.  You only have to learn two situations here.
DLD'L'D'F'DF
D'R'DRDFD'F'
Q: What if the edge is in the right spot, but flipped wrong?
A:  Insert a random edge in it's spot, and put it back in correctly.
On to the Last Layer