how do use a file as a soucre
If you use an online editor such as the SoloLearn CodeEditor you have to host the file on line and access it from your code by its url. For example you could use dropbox to have the file available online via url.
What kind of file is that?
music file I presume
To include audio files in an HTML document, use the <audio> element. You can write some text to display if the element is not supported by a browser. This text is not displayed if the audio is supported. example: <audio controls> <source src="source1.mp3" type="audio/mpeg"> Your browser does not support audio elements. </audio>