The Parts of a key.

This picture of a key shows the parts of the key and I'll list what the part it is and its primary function.

1. The Bow:  The bow of the key is the part that you hold on to when inserting the key into the lock. The shape of the bow varies from lock to lock and is also used to help identify the lock and key way that it opens. 
2. The shoulder: The shoulder of the key stops the key from being inserted into the cylinder any further than it should be. When duplicating keys on a machine, the keys should be aligned using this shoulder to insure a accurate key copy is produced. If the shoulder of the key is offset in any way the cuts will not align properly to their coordinating hole and could cause the key not to turn the cylinder.  
3. The cuts: The cuts of the key are very important. The cuts of the keys are spaced and cut to the necessary depth to turn the cylinder. These spaces and depths depend on the type of lock you are working with.
4. The tip: The tip of the key should look like a ramp, smooth and at a angle. The tip is used to raise the pins and the shape allows the key to be inserted with ease. If the tip was flat and blunt it wouldn't pass the first pin and be difficult to insert.  

All the parts of the key play their own parts in turning the cylinder of a lock.