The audio buses in Fabric provide a method of controlling the volume, pitch, setting Unity's audio mixer group and limiting the number of voices.

To create a new bus enter the name of the bus in the text field and click on the "Add New Bus" button.

To assign a bus into a component just select the name of the bus from the drop down menu in the component inspector,

NOTE: If an AudioMixer Group is already set in the component it will take precedence over the Audio Bus mixer group selection