Gravity is a force that gives weight to objects on Earth and makes them fall or attracts them toward the Earth’s centre of gravity (somewhere inside the core). It is the same force that keeps our Solar System together, because all the planets of our system are attracted by the huge mass of the Sun, and orbit around it.
Gravity is proportional to mass. The mass of the Earth gives it gravity: rockets need a lot of energy to overcome the pull of that gravity. If we were on a lighter planet, like Mars or Mercury, we would feel a lesser gravity field: compared with the Earth, our bodies would feel very light, and we would be able to jump many meters easily.