Step 1: Knowing thy lock.
First of all, there is a dial, a body, and a clasp (The U shaped thing on the top that comes out when unlocked).
When you open your lock you would normally spin the dial right a few times to reset, then go to your first number. Then, you would turn left, passing your first number once, then stopping on your second number. Finally, you would turn right again to your third, and final number and pull on clasp.
Okay, now you know thy lock.