It sounds as if you have little or no experience. So.....
Typical
mixer, is divided into chanels and has a location to
plug in a cable form an input device. This can be a mic cable, 1/4"
TRS (tip, ring, sleve),
RCA (stereo jacks). The
mixer is then going to control certain peramiters of the signal as it moves throught he
console.
Usually the first adjustment is the "master" volume. This can be labeled as
trim, sens, or
gain. This knob is most often located at the top of the chanel strip. You should see several knobs between the
Trim knob and the
fader. These will be for EQ and Aux sends. EQ will adjust certain frequencies to add or remove highs and/or lows to your preference. Aux sends are used to
send signal to another device such as a
reverb unit or a
monitor system. Then at the bottom of the
channel strip should be the
fader which makes fine adjustments to the volume during a performance.
This is a very basic start. If you have other questions don't hesitate.