Well, this is the most necessary and initial part in android development. One should have knowledge about creating an Activity. It represents a single screen of your application, for more details check this Article on Activity and Activity Life Cycle Every activity in android consist two files. One is JAVA file and another is XML fie. JAVA file helps you implement the functionality of components that you defined in your XML file. To create an layout you should have an XML file. This is the file where you create an user interface for your activity. There are two approaches to create an Activity: 1. Create both the files(JAVA & XML) separately and define it in Manifest file a) In android studio, Select File Tab and click New
Learn Android tutorial Android Basics in Kotlin, Advanced Kotlin, Kotlin Fundamentals, Android Developer Fundamentals (Java)