please explain this equation!?

I assume you mean

F=G*m1*m2/r^2

In that case,

F is the force due to gravity between two bodies

G is the universal gravitational constant

m1 is the mass of the first body

m2 is the mass of the second body

r is the distance between them

Is the equation you are speaking of F=GMxM/r^2? If so this is Newtons law of universal gravitation. It means the force of gravity that two objects exert on each other is equal to G (the gravitational constant) times the mass of one object, times the mass of the other object, divided by the distance between the objects squared. When speaking of the gravity of two objects, the force of gravity one object exerts on another is the same as the other object exerts on the first no matter what the mass. The greater the distance between the objects the weaker the force. I'm sure there are better ways explaining this but this is the gist of it.

Read sect. 4 here: http://en.wikipedia.org/wiki/Newton%27s_law_of_uni...

BTW, what you wrote makes no sense: GM2/r is not Newton's or anybody else's equation. An equation has an = sign, all you have is a bunch of symbols: meaningless.