When I start using an app on Facebook, the app shows "10K people using this app", but before to do that I need to "subscribe" to that app (click a button telling me that I'm going to be using that app) How do I do that with my own app, so I can keep track of the amount of users using it?
Besides, when someone starts using my app (an online magazine) I want to update their activity with something like "John Doe is Reading < Name of the App >"
What elements of the Facebook API do I need to achieve such behaviors?