Open the file on your computer make sure it ends with .mp3. If it ends with something else, then you need to convert the file to MP3 format. There are many free online audio file converters and audio programs to do this.
Open the directory that contains all the files for your website. This usually is done by using an FTP client, although there are several other methods. Once you have opened the directory, copy the MP3 file into that directory. Make a note of the file name.
Open the home page of the website in your browser. Look for the file name on the end of the URL, which usually is displayed as "index.html," "home.html" or something similar. It is everything that comes after the "/." Delete the file name, and replace it with the file name of the MP3. This is the URL that links to your file. You can email the URL to people or post it onto sites so that people can listen to your music.