Endgame 101 - Outflanking
Once you understand the opposition, it's time to learn all about outflanking. Outflanking is a way to use the opposition to make forward progress with your king. If we start with our simplest example of opposition with Black to move:
White has the opposition and can easily reach the back rank. After 1...Ke6 White can outflank by 2.Kc5, making forward progress toward the back rank. If 2...Kd7 then 3.Kd5! regains the opposition. 3...Kc7 4.Ke6 (outflanking again) Kd8 5.Kd6 (regaining the opposition) Ke8 6.Kc7 (outflanking one final time) and now nothing can prevent White from reaching the back rank.
If you want to make forward progress, you should first gain the vertical opposition on the file you wish to outflank around. In the above example, White has vertical opposition on the d-file, and will outflank on either the c- or e-files to make forward progress, regaining opposition on the d-file to outflank again.
Here is a test problem to test your knowledge of the opposition and outflanking.
White is to move, and your task is to reach one of the green squares. Really try to work this out before reading the solution. When you've mastered outflanking, it's time to learn about key squares.