A force is a push or a pull. A force can give energy to an object causing the object to start moving, stop moving, or change its motion.
Forces occur in pairs and can be either balanced or unbalanced.
Balanced forces do not cause a change in motion. They are equal in size and opposite in direction. If you compete against someone who is just about as strong as you are, there will probably be a time when both of you are pushing as hard as you can, but your arms stay in the same place. This is an example of balanced forces. The force exerted by each person is equal, but they are pushing in opposite directions, in this case together.