Plug all microphones into the different channels on the back of the mixer. The microphones should connect with an XLR cable into the XLR jacks. XLR jacks are large, round outlets that have three small holes inside, laid out in a triangular pattern. Guitars can connect to the 1/4" circular line-in jack. Any MIDI devices should connect to the MIDI ports. MIDI jacks are round outlets (smaller than XLR) and have five or seven holes laid out in a semi-circular pattern.
Connect a cable from the jack labeled "Alt Output" (also called "Subgroup Out") to the computer's sound card. You may need a 1/4"-to-1/8" converter to plug from the fatter plug that mixers use to the skinny input that a sound card has. Or you may need a separate audio interface in order to connect your mixer to the computer. This will depend on what type of sound card your computer uses. Using the Alt Output jack allows the sound that is manipulated by the mixer to be sent to the computer for further manipulation and recording.
Connect a cable from the computer's line-out jack to any of the mixer's available audio channels. Connecting a line-out channel to the mixer allows the audio sent to the monitors (and headphones) to reflect any adjustments or effects you made within the computer program.
Connect cables from the left and right "Monitor Output" channels to the studio monitors. Also connect the headphones to the "Headphone" jack on the mixer for headphone monitoring to the musician.
Turn on the mixer and launch an audio-editing program on the computer.
Begin playing the instruments and asses the output coming from the monitors. Adjust the knobs on the mixer as desired. Also place any effects that you wish to incorporate into the audio (such as reverb) using the computer program.