In the patch panel each audio track has a small square box with a number. That number is the audio input that is matched to the numbers at the bottom of each audio strip at the bottom of the audio desk.
To map audio tracks:
An audio track input is selected.
If the input channel box is empty, the audio track is not patched to an audio desk input. You will not hear audio segments for that track.
Normally all these mappings are automated. It is important to understand these outputs are either the audio channel outputs for your hardware or discrete channel outputs for files exported to the application.