Explain what is meant by the equation :
$g=G\times \frac{M}{R^2}$
where the symbols have their usual meanings.

g = GM /R²
This is an equation , which expresses acceleration due to gravity. It states that acceleration due to gravity (g) can be calculated as a product of the Gravitational Constant (G), which is 6.673 × 10⁻¹¹ Nm² kg⁻² and mass of the planet (M) i.e., 5.98 × 10²⁴ kg in case of the earth divided by square of radius of that planet (R), i.e., 6.4 ×10⁶ m for earth. This is an equation, which expresses acceleration due to gravity. By putting the respective values for earth, g can be calculated as 9.8 m/s².