Gravity is force that attracts us and any other object towards earth’s center. When we jump gravity pull us back and we fall back on earth. There is a difference between gravity and gravitation. Gravitation is the force of attraction between objects and gravity is the gravitational force between earth and other objects that means gravity is special case of gravitation.
On the earth gravity keeps air around us from escaping into space. Tides into the ocean are caused by the gravitational pull of moon and sun. By knowing gravity you can calculate when a ball will touch the ground after released into air. You can measure and graph the trajectory of a projectile. You can calculate how much propellant is required to push a rocket into the space and many more.
Gravity at the surface of earth is 9.8 that means an object falling towards earth gains 9.8 m/s speed in every second if air resistance is neglected. If a ball is dropped from a building it will have 9.8 m/s speed at the end of 1st second, 19.6 m/s at end of 2nd second and 29.4 at the end of 3rd second and so on. Value of gravity decreases for an object which is going away from earth or going closer to the center of earth. Gravity at the center of the earth is zero. Every object is accelerated at the rate to earth no matter it is a paper clip or paper. If two masses are dropped from a height both will hit the ground at same time. You are thinking why a paper falls slowly than a paper clip when both are dropped from same height? It is because of air resistance, paper clip has lower surface area than paper so resistance for paper is high. If you drop both paper and paper clip into a vacuum chamber both will hit the bottom at same time.
Gravitational force exists since the formation of universe. It is the fundamental force of nature. It is the force that attracts atoms together to form stars and planets. It keeps the moon in orbit around earth and earth around sun. How high is the gravitational pull between two objects? It depends on mass and distance between two objects. Larger the mass and less the distance greater would be the gravitational pull.
Sir Isaac Newton was first who mathematically defined gravity and gave law of universal gravitation. But later, Albert Einstein made improvements to it in theory of relativity because in some cases newton law of universal gravitation was inaccurate.