Upnp
Upnp is a protocol for remote controlling a music/video player over a network. Commonly it's found in TVs network media players and software like Kodi. If you use a controller like BubbleUPnP you can control the renderer remotely.
After you have enabled UPnP as your localplay instance you need to find a renderer to serve to.
With BubbleUPnP you can search your local network and find your local renderer.
For example; there is a local renderer on my network running on Kodi so the URL for my Upnp instance is:
http://192.168.1.18:1221
You can then also try and load that link in a browser and you should be getting an XML response.
Now that you've found a local URL on your LAN you can try playing from the Ampache UI!