How can two apps interact

Question

I’ve been thinking of a concept that seems bad on paper if the software doesn’t work as I want it to. The idea centers around two apps communication. Like when we use twitter or gmail to log in a mobile game, we often get an email saying ‘hey, is this you’. I was wondering if there’s a way to make a different application to run in the back ground and while you do certain actions in a different app the app running in the background can send like notifications saying “great job” or something like that. Can someone point me in the right direction or tear my idea apart.

Answer 1

For those actions, your app sends a request to the server. And the server emails to the user.

Answer 2

google: API (api)