[1] It works by having its slewing axis parallel, or almost parallel, to the Earth's polar axis so that the attached dish can follow, approximately, the geostationary orbit, which lies in the plane of the Earth's equator.
[2] They are also used in other types of installations such as TV, cable, and telecommunication Earth stations although those applications usually use more sophisticated altazimuth or fix angle dedicated mounts.
[3] Polar mounts can use a simplified one axis design because geostationary satellite are fixed in the sky relative to the observing dish and their equatorial orbits puts them all in a common line that can be accessed by swinging the satellite dish along a single arc approximately 90 degrees from the mount's polar axis.
This also allows them to use a single positioner to move the antenna in the form of a "jackscrew" or horizon-to-horizon gear drive.
But when observed from other latitudes the fact that geostationary satellites are at a fixed altitude of 35,786 km (22,236 mi) above the Earth's equator, and vary in distance from the satellite dish due to the dish's position in latitude and longitude, means polar mounts need further adjustments to allow one axis slewing: