Great, just two further questions for you.
How and why do two concentrations of mass-energy separated by space attract each other?
"Why" is a metaphysical question that is beyond the scope of physics. "How" is an enormous question, but there are several very good answers. I can't give you a complete answer, because that would require several graduate-level courses in physics, but I can give you a sketch.
The simplest way to think of it is with the Newtonian concept of the gravitational field. Everything with mass has a field associated with it, that extends to the furthest reaches of space. Masses that find themselves in the field will, in the absence of other forces, move so as to minimize their potential energy with respect to the field, which means that the masses move closer together.
Einstein showed that the gravitational field can be conceptualized as a curvature of space and time. The attraction then becomes an extension of Newton's first law of motion: objects at rest will remain at rest unless acted upon by a force. Objects that are in freefall are simply remaining at local rest in their inertial frames; the attraction results from the fact that (thanks to the curvature of spacetime) the local inertial frame is accelerating towards the attractive mass. This concept implies several experimentally testable consequences, and these have been verified exhaustively.
But that's not the end of the story. It is fully expected that it will someday be shown that the gravitational field is quantized, i.e., that it can be decomposed into carrier particles known as "gravitons", much the same way that the electromagnetic field can be decomposed into photons. No workable, testable quantum theory of gravitation has been devised, but there is reason to believe that we will have such a theory within the lifetimes of most of the people alive today. I think we're close.