Volumio: What does 'source' do?

What does the Source button on the bottom of the player pane do? Right now, the drop down list is empty…

depends on your media device. If your device allows you to change its ‘source’ / ‘input’, you can use that to change it. Example, my TV has 4 hdmi inputs, HDMI1, HDMI2, HDMI3, and HDMI4. I typically have to click the input button on the remote to change from HDMI1 to HDMI2. Instead, you can use that dropdown. In my example, it would be a dropdown containing HDMI1, HDMI2, HDMI3, HDMI4.

There may be other uses for that dropdown, I haven’t ran across anything else though.

Okay for Volumio the source allows to start playlists.

Yes, the sources listed in the device state attributes are a list of the playlists you’ve created in Volumio.