Your Yapp ID is the unique identifier for your published Yapp.
There are a couple different ways to get one so that you can load it up in the Yapp container app:
Go to http://yapp.us on your computer or iPad browser and create an app of your own, or edit an app if you’ve already created one. Once you click "Preview" or "Publish" for the first time, your app will have a Yapp ID, which you can find at the tail end of the URL beginning with http://my.yapp.us/[YAPPID] (See picture below.)
If you've been invited to download a Yapp by someone else, contact the event organizer for the Yapp ID of the app.
If you have installed a Yapp on your device, you can find the Yapp ID in the sidebar.
If you want to check out a demo app to get you excited and ready to Yapp, enter "CONFERENCE" into the Yapp ID field in the Yapp mobile app.