Instructions: KGS Game Setup
After you log in your KGS account, you will see "Custom Game" in the upper right corner (see the picture below), then press it.
After you press "Custom Game", a small window will show up:
change "Demonstration" to "Free" (see the picture left).
change the "Rule Set"to "AGA" (see the picture middle).
change the "Time System" to "Byo-Yomi" (see the picture right).
Before you press "OK", make sure the "Handicap", "Komi", "Main Time", "Byo-yomi Time", and "Byo-Yomi Periods" are correct. You can easily change these settings by clicking on the "+" and "-" signs. If everything is correct, then press "OK" (see picture below).
After you press "OK" the game will appear on the list (see picture below). Then wait for your opponent to join your game.
When a player joined in your game, you will see his/her username. If it is not the right player, you can click "X" on the right side to remove this player. If it is the right player, after confirming with "Rule Set" and "Time System", then press "OK".
Optional: you could change the stone's color by clicking either black or white stone (see picture below).
After you press "OK", you will see the "check mark" and "Waiting for Acceptance" on the top, then wait for your opponent to press "OK" on his/her side (see picture below). Once your opponent presses "OK", the game will automatically start. Then you are all set and good luck!