The 2nd Law of Motion states acceleration is produced when a n unbalanced force acts on an object (mass) The more mass the object has the more net force has to be used to move it.
Examples:
If you use the same force to push a truck and push a car, the car will have more acceleration than the truck, because the car has less mass.
It's easier to push a empty shopping cart then a full one, because the full one has more mass than the empty one. This means more force is required to push the full shopping cart.