The pressure gradient force is the force that is usually responsible for accelerating a parcel of air from a high atmospheric pressure region to a low pressure region, resulting in wind.
The pressure gradient force acts at right angles to isobars in the direction from high to low pressure. The greater the pressure difference over a horizontal distance, the greater the force and hence the stronger the wind.
However the pressure gradient force is not the only force that acts on a moving parcel of air — if it were, then eventually the low and high pressure regions would disappear. The second force acting on a moving parcel of air is the Coriolis force.