Anyone got a thread that shows how to install bagged suspension & how much they are for the back rears?

Kk i've just done a bit more reading & with the coil spring setup it apparently Keeps the coil spring & then the airbag sits inside the spring..Does this mean there is no more shock absorber required? & if i did decide to have it lowered with air bags Do i keep stocky springs in there and use the airbags & dump it ? Because if i chuck lowered springs in the car & then have airbags which would be higher then the actual lowered spring the spring would be floppin around?