Mass resists forces (inertia)
An object's mass describes its tendency to resist changes to its motion or state of rest. This tendency is called inertia.
This means that a force must be applied to change the motion of an object.
A spaceship travelling through space will not slow down unless it experiences a force.
Similarly, a force must be applied to get a stationary object moving.
A stationary ball remains at rest on the ground until it is kicked.
An object with a larger mass requires a larger force to change its motion.
A larger force is required to lift a bowling ball than a ping pong ball. The bowling ball has more mass than a ping pong ball.
Inertia itself is not a force.