First, upload a mix of your performance with the existing music, so people can hear what you’ve added in context. Then, include your individual tracks (voices and/or instruments alone with no backing, for example) in the Working File, so others can work with your part separate from any other tracks. You don't have to include all the other tracks since they're presumably available in the original contributors' Working File, but it never hurts to keep everything together in one place!
For more information on what a Working File is and how to upload one, CLICK HERE.
If you have any questions, please send us an email to firstname.lastname@example.org and we will get back to you as soon as possible!