Answer:
It is used to calculate
(i) force of attraction between two masses
(ii) the mass of earth
(iii) the value of gravitational acceleration ‘g’ above the surface of earth.
(iv) Orbital Speed of satellite
2: The prediction about the orbits and time periods of modern satellites are made on the basis of this law proved to be very accurate.
3: The prediction about the Solar and Lunar Eclipse made on the basis of this law proved to be very accurate.
(Newton proved that the force that causes, for example, an apple to fall toward the ground is the same force that causes the moon to fall around, or orbit, the Earth. This universal force also acts between the Earth and the Sun, or any other star and its satellites)
I hope this helps you:)