Flag messages received

When I receive 1 or more messages, for example, in What's App, let's say I received 3 messages. On top of the what's app icon, there is an orange "ball" with the number 3, in fact the amount of call. No Linked In the same thing and so goes for every app. I'm making an App, where the client will also get called by that App. How do I do this, ie how do I signal indicating the amount of messages received? Is there any plugin, dll or something similar that I have to load into my App? I'm waiting for some information.