Mass of Earth = M
acceleration due to gravity on surface of Earth = g
mass of satellite = m
altitude of satellite above Earth's surface = h
Earth's radius = R
distance of satellite from center of Earth = R + h
For any satellite to go around in a circular orbit, there should be a centripetal force that makes it go around in a circle. For a satellite, this force is supplied by the gravitational force of attraction (Newton's law).
let v = linear velocity of satellite along the circular orbit.
Actually the orbit is an elliptical orbit with very small deviation from circle. However, for a simple solution, we assume it as a circular orbit.