Sitting about 22,000 miles (36,000km) above the equator in a geostationary orbital position is a large number of broadcasting satellites beaming signals down to earth. These satellites spin at the same speed as the earth so appear to be stationary from earth. Due to the distance travelled by the satellite signal from earth up to the satellite and back there is a slight time delay of about a second in receiving the signal.
The curved (parabolic) shape of a satellite dish acts like a magnifying glass and reflects the signal that is being broadcast from these satellites to a focal point. At the focal point of the satellite dish sits an LNB (Low Noise Block). This universal LNB then picks up the radio waves that are being broadcast from the satellites and sends the signal down a cable at a lower frequency to a satellite receiver. The satellite receiver (sky box, sky+, freesat HD box are all basic satellite receivers) then converts this signal again; this time to be sent as a recognisable frequency to your television.
As long as there is a clear line of site between the satellite in space and your satellite dish you should always be able to receive a satellite signal. This large universal coverage makes satellite television an ideal solution to any body travelling around with a caravan or motor home; or somebody who lives in a poor aerial reception area. However as you move further away from the satellites footprint the satellite signal strength becomes weaker. This means a larger satellite dish is required to magnify this weaker signal strength.