For more info:
Step 1: Connect the Microphone(s) and Instruments to the Mixer
Locate the microphone inputs and line inputs and connect to these. Microphones commonly use XLR connectors while instruments and live-level devices use 1/4" connectors.
Step 2: Connect the Main Outputs
Connect the main mix outputs to your power amplifier(s) or powered speakers. Many mixers have XLR-type connectors for main outputs. Others have 1/4" tip-ring-sleeve balanced connectors.
Step 3: Connect to Monitors
Most mixers have at least one auxiliary output labeled AUX SEND or MONTOR OUT (or perhaps just AUX) that allows you to connect a monitor system or other equipment. For monitor connections, use a pre-fader AUX out (often AUX ONE). This is usually a 1/4" connector and is connected to the input of a power amplifier(s) or powered monitor speaker(s).
Other uses for AUX outputs are: Connecting effects units and connecting recording devices. In the case of effects units, these are fed a signal by the AUX output and then the treated signal is connected back to the mixer through the mixer's RETURNS.