Gravity is force that pulls towards the center of the earth. without gravity, we would be floating around and it would be hard for us to get items that we drop easily. the force of the gravity keeps all the planets in order and orbit around the earth.
for example, our gravity pulls the moon causing the moon to orbit around the earth.
in other words, it is a force that pulls all matter. because of the sun's strong gravity, it allows the planets to orbit around the earth.