An amateur radio satellite is an artificial satellite built and used by amateur radio operators. It forms part of the Amateur-satellite service. These satellites use amateur radio frequency allocations to facilitate communication between amateur radio stations. These satellites can be used free of charge by licensed amateur radio operators for voice (FM, SSB) and data (AX.25, packet radio, APRS) communications. They act as repeaters, as linear transponders, and as store and forward digital relays.
Learn more about AMSAT here.
Amateur satellites can be worked using simple hand held or fixed antennas, although you will probably find the best results with a beam either hand held or mounted on a AZ/EL rotator.
When working satellites you will have to account for doppler shift. This is an affect on the signal because of the relative speed of the sat as compared to the fixed earth station using (or working the bird) the sat. The sat is orbiting the earth at a speed high enough that it will appear to be on a higher frequency as it approaches the earth station, then as it moves away the freqeuncy will shift down to a lower frequency.
Learn more about Doppler Shift here.