Gravitational force is a force this is present everywhere in this universe. it is force which attracts other things towards it. this force is directly proportional to the mass of the body. everything in this universe have mass and have its own gravity even we the humans have our own gravity. but as I said that it depends upon mass that's why we can't attract other things on this earth towards us because mass of earth is much more than us.
we are able to stand sit and do our daily life works because of we walk run sit etc due to gravity.suppose if there was no gravity than we will remain in the air and not able to do our works fast as we can do know.