Hold the cube with the solved first layer on the bottom
Find a top-layer edge piece with no yellow color
Match that edge’s front color with the center color of the side it belongs to
If the edge belongs on the left side, use:
U’ L’ U L U F U’ F’
If the edge belongs on the right side, use:
U R U’ R’ U’ F’ U F
Repeat until all four second-layer edges are inserted
If a second-layer edge is in the middle layer but in the wrong spot, remove it with one of the above algorithms first
If a second-layer edge is flipped incorrectly, remove it and reinsert it correctly
Keep the first layer intact while solving the second layer
After all second-layer edges are solved, move on to the top layer