Even with gravity, if the intended satellite goes too fast, it will eventually fly away. On the other hand, if the satellite goes too slowly, gravity will pull it back to Earth. The orbital velocity of the satellite depends on its altitude above Earth. The nearer Earth, the faster the required orbital velocity. That orbital speed and distance permits the satellite to make one revolution in 24 hours.
Geostationary orbits are ideal for weather satellites and communications satellites.
Note that the moon's orbital velocity is slower because it is farther from Earth than artificial satellites. To get a better feel for orbital velocities at different altitudes, try NASA's orbital velocity calculator. To learn more about orbits and other topics in space flight, try JPL's Basics of Space Flight Learners' Workbook . A detailed technical treatment of orbital mechanics can be found at this company's site . In general, the higher the orbit, the longer the satellite can stay in orbit.