G ravity is a force that pulls any two objects toward each other. Though we commonly think of gravity as something of the Earth, it is much more. Drop a red ball from the top of a building and, if there were no influence from the wind, the ball would be closer to the building when it landed on the street below than it was when you let go of it. The building exerts a gravitational pull on the ball. A small lead ball would have more mass than a large balloon.
Gravity decreases with distance.
The Earth, for example, exerts enough gravitational pull on the Moon to keep it in orbit. On the other hand, the Earth exerts very little gravitational pull on, say, Pluto. These two objects are the same size, but the red one has more stuff in it, so it has more mass. Its gravity is stronger, so it pulls the blue object toward it. But the blue object has mass, too, so it exerts a smaller amount of gravity, pulling the red object slightly.