Connect the audio interface to your computer using the Firewire cable. An audio interface acts as an intermediary between incoming audio signals and the designated digital audio workstation. You can find dedicated audio interfaces at most audio electronics stores.
Connect the microphone to the audio interface using the XLR cable. This connection allows the microphone to pass received audio directly to the interface. The XLR port on the interface should be clearly labeled; if not, consult the interface's documentation.
Launch your digital audio workstation and create a new audio track. In the "Settings" menu, select the audio interface as the designated audio input mechanism. Adjust the I/O settings of the audio track to receive audio from the interface.
Play the acoustic guitar next to the microphone. The microphone will capture and route the sounds of the acoustic guitar directly to the computer. When you play the guitar, the audio will play through the computer's speakers. Click "Record" to start recording the acoustic guitar.