On the right click the latest version in Releases and download the zip file. Extract the exe file to a location of your choice.
To make it easier to use, as it is a command line tool, you can add the location of the executable to your PATH environment variable.
In the terminal of your choice, navigate to a location you would like to download the files to. Then run the following command:
YoutubeAudioDownloader.exe [URL]
It will then download the audio to the location you are in (if you have it added to the Environment PATH).