Attenuator ...??

I am fairly new to trying to capture good audio and still learning about things other than a mic and mixer. This is going to be a very open question and don't have a real specific application for it yet but I was hoping someone could give me a real basic explination for an Attenuator(such as Audio-Technica AT8202 Attenuator). And what it's used for. Or maybe a web site I could look it up myself.

Any info would be appreciated,
Bret