NikTheOtaku Hi!
You need a direct URL to an MP3. For example: http://www.url.com/songtitle.mp3
If you've been trying youtube, it won't work.
If you have mp3 files of your songs on your computer, you can find a music uploading site where you can upload them, and obtain a direct link to the song online. If you want to grab an mp3 from a youtube video, you can do that too, by searching 'online youtube to mp3 converter'. Then you'd have to upload it after it saves to your downloads folder.
There are other alternatives as well. Check this thread: https://drrr.chat/d/327-question-about-playing-music
The site can also support: music.163.com, xiami.com, y.qq.com, bilibili.com