There are three laws that form Newton's Law of Motion.
The First Law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change it's state by the action of an external force. This is often used as a definition of inertia.
The Second Law says that acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated), the greater the amount of force needed to accelerate it.
The Third Law is that for every action there is an equal and opposite reaction.