Probably the most important thing to know, when picking a lock, is how the lock works. The common pin-and-tumbler has 3 main parts- a hollow, outer cylinder- - the tumbler (the inner cylinder) – and a set of pins. The pins are varying lengths and each pin sits in a shaft, running through the tumbler and the outer cylinder, to prevent the tumbler from turning. All of the pins are in two pieces, a top and bottom section, when the key is inserted the seam between the top and bottom pins align with the seam between the outer cylinder and the tumbler. When the seams are aligned the tumbler can be turned and the lock is opened. When picking a lock you have to use a pick to move all of the pins into the correct position while keeping tension on the lock with a tension wrench.