Insert the 1/8-inch audio cable into your computer's audio output jack. Insert the 1/4-inch side of the cable into an audio input jack on the sound mixer.
Insert a 1/4-inch speaker cable into "Main Out" jack of the mixer. Connect the other end into the "Audio Input" jack of the speaker.
Plug the audio speaker into an electrical outlet. Turn on the audio speaker with the power switch and turn on your computer. Turn up the "Master Volume" knob on the mixer along with the volume knob for the audio channel used by the computer.
Open your computer's "Sound Preferences" application. Make sure the audio port has been set to "Sound Output" and not "Sound Input." This setting will enable the computer to send an audio signal to the mixing board.
Open a recording application on your computer. Press the "Record" button inside the application. Your computer's microphone will begin recording sounds and all these sounds will play through the PA speaker. Be sure to keep the PA speaker at least 10 feet away from the computer microphone to avoid feedback.