Layers allow you to access more channels than the physical faders.
To use layers:
Press the layer button you need (Ex. A, B, C, D)
The faders will change to control different channels.
Check the channel names on the screen.
Adjust the desired channels.
Examples:
Layer 1: Most used channels (main mics, computers).
Layer 2: less commonly used channels (spare mics, etc).
Layer 3: random stuff like recording equipment or balconey monitors.
Layer 4: inputs on back of mixer.