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Moderator Note
I agree. We are not being asked to write the essay!
It is energy that bends space-time. And (as we know from E=mc2) mass and energy are equivalent.
Gravity is just how we perceive this curvature of spacetime. It causes things to move together, even in the absence of a force.
One analogy that might help, is to consider two people separated by a few miles and both travelling due north. As they get closer to the North Pole, they will get closer together (following the lines longitude). But nothing is pushing them together, it is just the curve geometry of the Earth's surface.
It is just an analogy to visualise something that is stretched and curved (and even twisted) by the presence of mass.
Even without understanding the math, you might get something out of this description of how the equations work: http://math.ucr.edu/home/baez/einstein/
(If you find it confusing, don't worry. It is!)