In a lot of league play when playing 8-ball, you must mark your pocket with some item so as to avoid any misunderstanding about exactly in which pocket you are trying to shoot the eight.
In some leauges it is against the rules to use any form of weapon, any representation of money, or table chalk.
In order to avoid this issues chose a pocket marker from below.
Simple to use: In most leagues that rquire a pocket marker you just place the pocket marker by the pocket you intend to pocket the eight.
Ensure your pocket marker doesn't not interfere with the pocket as this could cause you to miss the shot and you will not have any recouse or in some leagues if it hits your pocket marker and you still pocket the ball, in some very strict leagues, it can cause you to lose the game.