If you want to create an app displaying on the screen “Hello world!” (a standard text for the first application), just… start a new project in Android Studio. It already includes Hello world! functionality. But what to do to display “I’m the best!” instead?
There are two ways of doing it: very simple and… recommended one (but still simple). Firstly, you have to start a new project or open the one created in Lesson 0 and then find again activity_main.xml file in layout subfolder (you could learn how to open that file from Lesson 0). Now click Text tab at the bottom of the activity_main.xml file window. You should see the code of layout of your first app.