How does gravity work?

Well gravity is something that keeps us people from floating off into space its just like if you sit a apple on a table some times it roles right and some times it doesn't but say their was no gravity that apple will float right up into space

Gravity is a force pulling together all matter (which is anything you can physically touch). The more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull more strongly. Mass is how we measure the amount of matter in something.