different types of rear shock suspension and their uses? explain me about the rear suspension of mountain bike.
Here is a very rough answer to your very generic and open ended question:

A rear suspension (or shock), together with the front suspension (fork), allows the bike to handle more terrain roughness. This gives you:


safety
traction
ability to go faster


The main two types of rear suspensions are:


air sprung
coil


Generally air suspensions are lighter and better for XC, all mountain, enduro. Coil shocks are heavier, more linear and better for downhill. See What&#39;s the difference between All-Mountain, Cross Country, Freeride, Downhill bikes? for a reference on mountain bike types.