Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

where:

F is the force between the masses,

G is the gravitational constant,

m1 is the first mass,

m2 is the second mass, and

r is the distance between the masses

Assuming SI units, F is measured in newtons (N), m1 and m2 in kilograms (kg), r in meters (m), and the constant G is approximately equal to 6.674×10^−11 N m2 kg^−2.

It's not sucking and it's not pulling. It's simply attraction. Force means how much they move. Newtons is a unit of weight, and this is how we can determine the force gravity is pulling on an object. Therefore, it is a unit of force. Kilograms is mass, newtons is weight, pounds are weight. Hence, you get things like, "A pressure of

*x* pounds per square inch." The pounds (unit of weight) is how much force is being applied to every square inch. There, you get a pressure lesson too.

This is Newton's law of course; Einstein changed up the rules a bit.

Edit: I felt like I should add this. Yes! Energy too. That was Einstein, again. Remember E = mc^2, where E is energy, m is mass, and c is the speed of light. This creates effects such as high energy causing gravity. In General Relativity, gravity is the warping of spacetime. This causes things to go faster (through space), and since time and space are a continuum, time will also be distorted (more as we approach the speed of light). Energy can warp spacetime as well. You could, hypothetically, shoot a laser with huge amounts of energy and warp spacetime in that direction. When approaching the laser, you would begin to get "carried away" in the "current" and time would slow down as well. This is a gravitational wave.