As Newton theorised back in the 17th century, every particle of matter exerts a gravitational pull on every other particle of matter. If you concentrate a large amount of matter in one place, it will create a much greater gravitational pull than a loose smattering of particles.
Mass is the measurement of how much matter is in a particular object. The greater the mass, then the more gravitational influence it will possess. Every planet, moon, star and galaxy in the universe has a different mass and therefore generates a unique gravitational pull.
The mass of the Earth pulls a falling object toward the ground at a rate of 9.8m/s2 (32.2ft/s2). In contrast, the mass of the Sun is 333,000 times greater than the Earth. As a result, a falling object near the surface of the Sun would be pulled downward at a rate approaching 274m/s2 (899ft/s2), 28 times faster than on our planet.