Gravitational force is an attractive force that act between bodies having mass.
Newton's law
Every body in the universe attracts every other body with a force, which is proportional to the product of the masses of the bodies and inversely proportional to square of the distance between them.
General relativity
In general relativity gravitation is explained on the basis of curvature of space-time.
For more details, please refer to the Gravitation Force.