In this animation you can view the motion of a small satellite (the green dot) orbiting around our planet, exactly above the equator, with a perfectly circular motion (in general a closed orbit will be ellyptical, but here we are examining the simplest case). The "camera" in this animation is placed above the north pole.
You can choose the period of the orbit, and as you know (you know it, right?), a longer period will cause the orbit to be larger. The shortest period you can choose is 1h32m50s, which is the period of the ISS (International Space Station) although the real ISS doesn't have an equatorial orbit.
While the satellite goes around our planet, our planet spins on its rotation axis, and when you choose a period equal to 24 hours the satellite moves together with the Earth. So, in that case, if you choose the option "Camera rotating with the Earth", you will see that the satellite doesn't move, that's why it's called geostationary orbit.
Look at what happens if you choose a period longer than 24 hours.