In step 3 of the first time setup process, you configure one track for each instrumental and/or vocal part you plan to play/contribute during sessions. Following is a video that shows how to assign inputs from your audio interface to tracks, and then indicate which instrument or vocal is associated with each track:
Configure Tracks Video
Note that you can change your track configurations at any time, including during sessions, so you are not stuck with just this one configuration. JamKazam will remember the last track configuration you used with your audio interface, and will automatically re-load and use this configuration in your next session from one to the next.
If you are having trouble getting your tracks configured the way you want them, please use the "Post a Public Question" in the right column of this page to submit a support request, and we'll be happy to see if we can help you get things working properly.