A basic android app helps learning about Fragments and the Navigation Component
A fragment is simply a reusable piece of your app’s user interface. Like activities, fragments have a lifecycle and can respond to user input. A fragment is always contained within the view hierarchy of an activity when it is shown onscreen. Due to their emphasis on reusability and modularity, it’s even possible for multiple fragments to be hosted simultaneously by a single activity. Each fragment manages its own separate lifecycle.