How to use golf ball markers?

If your ball is on the green and in the direct path of another player's line to the hole, you should mark your ball with Billy's rough ball marker. Most players will place the ball marker directly behind the golf ball and pick up the golf ball. The rules state that you can place the ball marker anywhere next to, in front of or behind the golf ball, but many players choose to create repetition and habit behind the ball
If your ball mark is obtrusive or might interfere with another player's shot, you can use the putter to measure from the ball mark to a point far away. Remember the steps you took in order to find the original location from which you picked up the ball.

Use the alignment golf ball marker
The updated rules for golf ball markings published in January 2020 deal with ball marking details, including sizing and alignment aids. Golf ball markers designed to aid alignment are legal as long as they meet certain size parameters. Most normal-sized ball markers with alignment lines are permitted; however, the equipment rules explain what is not allowed.

Ball machines with alignment aids (lines, arrows, etc.) must:
less than an inch in height
less than two inches in any horizontal direction
Do not measure or measure slope, green speed or any other condition
Any balloons exceeding the above dimensions and having alignment lines are considered "alignment devices" and are not allowed. The first time the alignment device is used to mark and align the ball, the player will receive a general penalty (losing a hole in the game and two strokes in the batting game). Second use results in disqualification.