Master Faders   

These faders control the level of signal going out the master outputs of the mixer, including any signals which may be coming back to the mixer via Aux Returns. 
In order to obtain optimum audio quality from the mixer these faders should usually be operated near design centre, roughly two-thirds of the way up. There is usually a marking of some kind to indicate this point such as shading or a zero.  The faders can be used to fade out a continuous sound or to make other level adjustments of this kind.