It absorb shocks.actually they dampen the vertical motion induced by driving ur car along a rough surface.if ur car only had spring,it would boat and wallow along the road until u got physically sick and had to get out.Or at least until it fell apart.
Shock absorbers perform two functions.firstly,they absorb any larger than average bumps in the road so that the shock is'nt transmitted to the car chassis.Secondly, they keep the suspension at as full a travel as possible for the given road conditions. Shock absorber keep ur wheels planted on the road.Without them, ur car would be a travelling deathtrap.Technically they are velocity sensitive hydraulic damping devices.In other words,the faster they move,the more resistance there is to that movement.They work in conjunction with the springs.The spring allows movement of the wheel to allow the energy in road shock to be transformed into kinetic energy of the un sprung road mass,whereupon it is dissipated by shock absorber.