Connect the USB cable to the USB port located at the back of the M-Audio recording device.
Connect the other end of the USB cable to any available USB port on your computer. USB ports are usually located at the back of the computer near the serial monitor port and A/V inputs and outputs.
Turn on the M-Audio recording device.
Go to "System Preferences" on your Mac. Click on "Sound" to open the audio preferences. Select the "Input" tab. There should be a list of all the audio devices connected to your computer. The name of the M-Audio device you connected should appear in that list. For instance, if you are using M-Audio's Fast Track Pro, that will appear in the audio device list.
Go to the "Start" menu on your PC. Click on "Control Panel," select "Sounds and Audio Devices" and click on the "Input" tab. Select the appropriate M-Audio device.