how to find the gravitational constant ? a long-winded answer will be more appreciated.

you need not find the gravitational constant since it was already found out by a scientist called henry cavendish , you just need to remember the value of gravitational constant as 6.673*10^-11nm²/kg².this gravitational constant applies to all the objects in this universe and never changes. so you need not find this.but you can apply this to find the force of gravitation between 2 objects and acceleration due to garvity(g).