Integration with mobile app

We are developing native mobile application for Android and iOS and we want to integrate discourse into it for online discussion forums. How our app will work is when the user logs in into the app, the user will also be logged in into the Discourse (through use of some kind of Discourse’s api). And, then the user clicks on Discussion tab inside the app and it will show the forum posts (through use of api).
Can anyone guide me on how to start with this?