Well, all masses attract each other (don't ask me how THAT actually works), the bigger the masses, the stronger the attraction.

But it takes a bigger force to move (more precisely to say: to change the speed and direction of movement of) an object with a big mass. That's why a big stone, which is much harder to move, falls to the ground just as quickly as a small stone, which is easier to move but not attracted as strongly.

This is also why the ball moves towards the earth and not the earth towards the ball, though the attraction force is always the same on both sides between two objects - you'd need a much bigger force to significantly move an object like Earth.

 It's also because of gravity that the planets keep circling round the sun and don't fly away in a straight line (without changing speed and direction) into open space.

We are told by people much smarter than us to visualize space being 'warped', 'downward', by a mass (such as the Earth).  They tell us to visualize pressing down on a bed, causing a nearby marble to fall into the depression.  Any mass nearby the Earth in space, especially one very nearby, such as a rock a few feet off the surface, is drawn nto this 'gravity well', and falls through space to the Earth. 

The honest answere has to be that NO BODY knows how gravity works. We only seem to know what it does. Your likley get into a philosophical debate on such tricky matters as oposed to the pragmatic scientific way which is to observe and measure a phenomenon, give it a name, but not necessarily understand it. A similar thing could b said of electricity and magnetism.