and Why do I need one and how do I use it?

In analog circuits terms, an attenuator is just a resistor. Attenuation is the inverse of amplification--it's the process of decreasing the amplitude of a signal.

Microphone attenuators are simply resistance in the microphone signal pathway chain. They turn down the sound. Many camcorders feature a "mic atten" switch to help keep audio to desired levels in loud environments--concerts, factories, etc.

Human-terms analog: Your parents telling you to "keep it down" when you were a rambunctious youngster were attenuators.

Ah Thanks I get it, so it creates impedance in line in order to cut volume? In computer networks, attenuation is the lose of signal because of the distance of the cable creates too much resistance...I get it...now.