You can 'extend' your Project Madeira applications by implementing these 'extensions' to your code base. Do this from the main menu in Figure 1 below. From there, you can view the 'Extension Marketplace', as well as navigate to AppSource directly and auto-filter the apps by app (Figure 2). Once in AppSource, you can see all the available apps you can add to your application (Figure 3).
Figure 1 - Adding extensions to your code base
Figure 2 - the apps you can browse from the Microsoft AppSource store
Figure 3 - The navigation to AppSource, filtered for the specific application