If Song Requests are enabled in your channel you (and your users) can request songs by either requesting the full YouTube URL, or just the video ID.
If your song request has been successful TidyLabs will post a message to your chat.
If links are enabled in your chat room users can request songs using the full YouTube URL.
If links are disabled, your users can request songs by using the YouTube Video ID. The Video ID is the set of characters after the v=