Muscle

The action a muscle generates is determined by the origin and insertion locations. They are attached to the skeleton and move the body by contracting in response to signals from the central nervous system, contraction is achieved by the sliding of thin filaments. When skeletal muscle contract they either move parts of the body via their attachments to bones, or produce tension to oppose stretch or even to allow controlled lengthening.  During every motion every muscle has to perform different duties.  The most simple to understand is the agonist - antagonist relationship.
The agonist is the muscle which (shortens) performs the primary action and the antagonist is the muscle which (lengthens) opposes it.

There are approximately 639 skeletal muscles in the human body, here I will only name a few. Those are


Quadriceps
Hamstring
Glutes
Abdominal
Chest
Back
Biceps
Triceps