Beginner's Solution
Step 4: Orient edges

After finishing the first two layers, now comes the more complicated part: solving the last layer. As the first two layers are entirely solved, it seems like every move we make will disrupt what we had just built. However, cubers have developed some very effective method of solving the last layer over the years. Here is the most common method: orient the top to be all yellow colors, then permute the side pieces. And the first step to this method is to build a yellow cross on top ignoring the side permutation (if there is no cross yet). Hence, for step 4 and step 5, we ignore entirely the arrangement of stickers on the side, we just care about bringing the yellow stickers to the top surface.

There are 3 cases to solve a yellow cross on top.

Case 01: Flipping opposite edges; straight line.

F R U R' U' F'

Case 02: Flipping adjacent edges; L shape

F U R U' R' F'

Case 03: Flipping all four unoriented edges; Dot.

apply case01 or case02 to reduce it.