Upload a song to the server and create a download link of the processed song that vocal tracks are reduced and instrumental tracks are intact. The quality depends heavily on the type of song, and so use the app with discretion. In many cases, it will be good enough to enjoy.
The processing is computation intensive and may take a minute or so. Uploading to server is processed in the order that has been submitted. If the server is busy processing other request, uploading will be queued for its turn.