have u ever put a bowling ball in the middle of a trampoline then rolled some other smaller balls around on the surface? If not give it a try. This is a simplified way of illustrating how gravity works reletive to an objects mass. The surface of the tramp is like the fabric of space/time being curved by the mass of the bowling ball the other balls fall toward it because it's mass is greater. Does this explain why gravity works the way it does? Sorry no. So i guess Coelho's answer was the most direct one.
Still give the bowling ball thing a try it's just fun.