Use this when you want to submit a song that is already on the web. You need to have the full URL (web address) the song handy, which you can get by going to a web page that hosts the song, right-clicking it, and choosing "Copy link location". This is usually faster than uploading it straight from your computer.

This is a song you like, and it is available for reuse under a Creative Commons license that allows remixing and commercial use (no "ND" or "NC" material!), or it is in public domain.

This is a song you like, but it is only available for reuse under a Creative Commons license that does not allow commercial use, i.e., a license with "NC" in the name.