Android is designed to empower users and let them use apps in a intuitive way. To provide a good user experience, you should know how to manage component lifecycles.
https://medium.com/androiddevelopers/the-android-lifecycle-cheat-sheet-part-i-single-activities-e49fd3d202ab
* Part II: Multiple activities — navigation and back stack * Part III: Fragments — activity and fragment lifecycle * cheat sheet in PDF format