force
A force is a push or a pull. When you shove a door, kick a ball, or lean on a wall, you are applying a force. It answers the question: what makes an object start moving, stop, speed up, slow down, or change direction? The everyday picture is simply pushing a shopping cart across a floor.
A force is a vector quantity, meaning it has both a size (its magnitude) and a direction. Its SI unit is the newton (N); one newton is the force that gives a 1 kg mass an acceleration of 1 m/s^2. Forces cause acceleration: Newton's second law says the net force equals mass times acceleration, F_net = m a. A single object usually feels several forces at once (gravity, a push, friction), and it is their vector sum, the net force, that determines the motion.
A common confusion is thinking a force is needed to keep something moving. In fact a force is only needed to change motion, not to maintain it. A puck sliding on frictionless ice keeps going at constant velocity with zero net force. Forces always come from an interaction between two objects; there is no such thing as a force an object exerts on itself.
A medium apple weighs about 1 N, so when you hold an apple, you feel roughly the one-newton pull of gravity on it.
One newton is a small, everyday force, about the weight of a small apple.
A force is not a thing an object 'has' or stores; it is an interaction happening now. Once the push stops, the force is gone, though its effect on the motion remains.