Explain the universal law of gravity and it's calculate from as well as the value of g

According to the Newton's law of gravitational every object in the universe attracts every other objects with a force which is called gravitational force.This gravitational force is (i) directly proportional to the product of their masses and (ii) inversely proportional to the square of the distance between their centres.

Explanation:

Newton's law of gravitational is called the universal law because it is applicable to all the bodies either terrestrial or celestial having any shape,size,mass or at any distance apart with any medium between them,at any time(past,present or future).