It sounds like all the answers you are looking for could be found easily using the search function.
Its a pretty basic system. Pump leads to valves, valves lead to struts, struts send off excess into accumulators.
Common failure points include the following:
Accumulators: Probably the most common, causing the it to ride like a truck as they have collapsed, giving the compressed strut over bumps with nowhere to send the excess fluid.
Valves: As these get older, then tend to let off pressure causing the car to sag. It starts out as a mild drop after the car sits for a while, but they can also completely fail.
Other than being costly, it is a fairly straight forward system.