Gravitational Force →
Newton's Gravitational Law statement is a combination of three individual statements. These are
 The force between the twoparticle is directly proportional to the product of their masses i.e.
$F \propto m_{1} \: m_{2} \qquad(1)$
Where $m_{1}$ & $m_{2}$ are the masses of the particles.
 The force between the twoparticle is inversely proportional to the square of the distance between them i.e.
$F \propto \frac{1}{r^{2}} \qquad(2)$
Where $r$ is the distance between the particles.
 This force always acts between the line joining the masses.
From the above the equation $(1)$ and equation $(2)$
$F\propto \frac{m_{1} \: m_{2}}{r^{2}}$
$F=G \frac{m_{1} \: m_{2}}{r^{2}}$

Where $G$ is Newton's gravitaional constant and its experimental value $6.67\times 10^{11} \frac{Nm^{2}}{kg^{2}}$
Properties of Newton's law for Gravitational force →
There are the following properties of Newton's law for gravitational force
Gravitational force is always an attractive force.
Gravitational force is action and reaction pair and follows Newton's third law.
A Gravitational force is a conservative force.
Gravitational force is central force i.e. it is always acting along the line joining between two particles.
Unit and Dimensional formula of $G$
The unit of $G$ is $\frac{Nm^{2}}{kg^{2}}$
The dimensional Formula of $G$ is $[M^{1}L^{3}T^{2}]$