Laceration and crushing: the tissue is torn or compressed by the kinetic energy of the bullet. It is a low velocity injury.
Cavitation: this is a permanent cavity formed by the passage of the bullet. This is particularly defined in high velocity injuries.
Shock waves: pressure on the sides and in front of the bullet caused by the force of the travel of the bullet will push through tissue, essentially compressing it. This may happen at any velocity but is more common at high velocities. Fluid filled organs like the heart can burst from shock waves.
Injury analysis answers questions like...
What was the direction of travel for the bullet? What was its entrance and exit angle? If there is no exit wound, where is the bullet? What was the distance between the weapon and the victim or target?