Look at the mixer's control surface; the sliders and control knobs are arranged in strips, known as input channels, across the width of the mixer. Each strip allows you to control the audio signal for that channel. The two strips on the far left contain the controls for the output channels.
Move the slider on channel 1 upwards to increase the level of the audio signal sent to the output channels, and move the slider down to decrease it. When each channel receives an input from a guitar, piano or vocal, you can adjust the sliders to control the level of each sound source in relation to the others.
Twist the control knobs above the slider to adjust the EQ, or frequency, of the sound. There are usually two or three EQ knobs per channel controlling low, mid and high frequencies. They are equivalent to adjusting bass and treble on a Hi-Fi system.
Rotate the knob marked with "L" and "R" to move the audio signal to the left or right of the mix. With the knob moved fully to the "L" position, a sound signal passing through the channel will only be heard through the left speaker. This effect, known as panning, helps to create a sense of space in the final mix.
Adjust the "Gain" knob to control the level of the input source signal that the channel can apply effects to. This is not the same as the volume slider for the channel which controls the level of the signal that goes to the output channel strips. The gain control should be set so that the input signal does not distort even if the source--a guitar, for example--is at full volume.
Set the sliders on the output channel strips to control the output volume that can be heard through the speakers. These two channels are called the "Master Output" channels and can be routed to a recording device or public address system.