What happens when one force acts on an object

A force is a push or a pull that acts on an object. A force can cause a resting object to move, or it can accelerate a moving object by changing the object's speed or direction.

When only one single force acts on an object, the object accelerates in the direction of the force.

That means that either the object's speed in the direction of the force increases, or else the path the object is following curves in the direction of the force.