Find the small white arrow pointing downward at the top of your lock. Turn the dial on your lock either direction until the 0 is in line with the arrow. This is your starting position for opening the lock.
Turn the dial clockwise to the first number of your combination. For example, if your combination is 17-2-30, you would rotate the dial until 17 is at the top of the lock, in line with the arrow. The numbers will move in descending order past the arrow until you hit your number.
Stop on your first number, then rotate the dial counter-clockwise toward the second digit. However, don't stop when you reach the number the first time. Using the combination above, move the dial past 2, and then do another full rotation and stop on 2. If you accidentally pass it a second time, give the dial a few spins and start over from Step 1.
Rotate the dial clockwise once more to the last number in your three-number combination. In this example, that would be 30. Once you have stopped on 30, grab the lock and pull down firmly. The lock should open. If not, it's possible you may have gone slightly past one of the numbers. Try again, making sure to line up the lines as closely with the arrows as possible.
Remove your things from your locker and close it firmly. You may want to spin the dial on the lock a couple of times to make sure the last number of the combination is not still lined up with the arrow. Your locker will now be secure until the next time you open it.