Watch a Space Shuttle launch and you'll hear about "zero gravity" and "zero G", terms that make people think (incorrectly) that someone or something in orbit has somehow escaped Earth's gravity. Not so. Without gravity you couldn't put a spacecraft in orbit.
Imagine hitting a baseball across a ballfield. Picture the arc it makes as it goes off into the outfield. To hit a home run, you have to hit it higher, and harder, to make a bigger arc that takes it out over the fence.
Now imagine launching the ball using a catapult, a cannon, and finally a rocket. As you send it with more force, the ball arcs out higher and faster, and lands farther and farther away--across the street, out of the neighborhood, over your town, across your country, even across the nearest ocean.
Eventually, if you launch it high enough and hard enough it will sail right over the distant curving edge of the earth itself. Instead of coming down, it literally misses the surface, gravity pulls it down and it falls over the edge, and loops around our planet. It constantly falling and missing, falling and missing, falling and missing.
Now, if you think about it, you'll understand why low orbits have to be faster and high orbits have to be slower. And now you know why geostationary satellites aren't stationary at all, but moving in an orbit at the same speed the Earth rotates, held in place by gravity and opposing centripetal force.
Next time you see a rocket launch think about hitting a baseball really really hard so it flies right along side the spacecraft.No you know why, except for gravity, the rocket and your ball would go straight out into space, never to be seen again.