Class Kotlin

Good Morning! I already have the layout of my first activity. But I have the following question regarding the creation of my first class. Will I be creating this class in kotlin in my activity main? in the first fragment ? or do I need to create a new class (right click on project/new kotlin class/file)?

If you said about layout.xml, you can link it to activity :

override fun onCreate(savedInstanceState: Bundle?) {

Recently, Google recommends using View binding in the fragment
Also look at the Compose

What is the class for?

Considering activity and fragment - this is android class for UI