What is the main difference between tendon injury, ligament injury and muscle injury?

Alot. While mechanisms of injury to these structures may be similar and in many cases treatment may be similar they are very distinct anatomically and in terms of function and healing potential. So it would be important to know the location, type and extent of injury.
Healing. Ligaments connect bones to bones tendons connect muscles to bone muscles are muscles injuries will effect motor function or joint instability depending on which one is injured.