After you have started the app, you would get a new window which is the UI of the app.
Now you can use the appropriate buttons to use the app and play around. If you have identified any bugs, make sure to report them at Issues.
As this app is not a finished product and has just started it's journey to become one, most of the advanced features like, playlists, multiple queues, equalisers, etc. are not currently avaiable.
Check it out here.