Documentation for AppStudio
Is this what you are looking for?
Edit: Sorry about the previous short answer...I was having connection issues. There are other tabs at that location including
Guided tour—AppStudio for ArcGIS (Desktop Edition) | ArcGIS
Extend your apps and create custom apps—AppStudio for ArcGIS (Desktop Edition) | ArcGIS
which may help.
If you lose the link, you can find it by going to https://developers.arcgis.com/ and finding AppStudio under the Configurable Apps... list. Then at the bottom of that page (or that is were I found it) is "Learn" link that takes you to the first link I listed above. Not your typically location for help, so good to remember the developers page.
You could eventually get there from http://www.arcgis.com/features/apps/index.html but you would again have to do a bit of clicking.
