Matter is almost always grouped to form bodies, and this is helped by the gravitational force  acting among their masses, and the electrostatic force, acting among their electric charges. These two forces regulate the way in which matter groups, although grativy only produces appreciable effects on bodies which have an enormous mass (planets, stars, etc.).
The force of gravity
In the 17th century, Isaac Newton had the idea that any two bodies, like the Earth and an apple, or Mars and the Sun,  mutually  attract one another due to their mass and with a force which is greater:
a) the greater the mass of the two bodies
b) the shorter the distance between their centres (the nearer one is to the other)

Body B exerts a force on body A, which we express as force of B on A (F_B/A ). At the same time body A does the same on body B. The two forces F _A/B and F_B/A are equal. The attraction is mutual.

Gravitational force is caused by a property of bodies (mass) which means that they attract one another.

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