What are airbags people are talking about installing and what are the purpose of installing them?

Air bags go between the rear axle and the frame.

They are used to level the truck when you have a load.

Sometimes called "air springs". Help stabalize the rear of your truck with a heavy load.

Had AirLift (brand) bags installed recently. What's nice is you can inflate them when towing a heavy load (in my case a 12K lb fifth wheel), and then deflate them when going solo. I had the valves installed in my wheel wells, so when I crouch down to check/inflate the tires, I can also do they AirLift bags at the same time. If I had added regular leaf springs, they would have ALWAYS been in use, making for a rough ride when going solo.

Generally, springs have different ranges of suspension-- the first being the most gentle, and the latter being more harsh. Using suplemental air suspension increases the first/gentler range, making for a nicer ride generally.

Paul.

They are also a safty item found in the center of the steering wheel.

Women also come equipped from the factory with two. Some models are more effective than others. Some of the aftermarket ones are even adjustable.