Open android studio > File > New project > Follow New Project Wizard
Your UI is a 'layout' and is an xml file in your resources folder. Double click it and drag/drop UI Components wherever you want on it.
You make stuff happen with your 'Activity' which is your only java file.
Link your UI and Java code by specifying a method you want called with the onClick of whatever button you're clicking.
The hello world app is created for you just by completing the wizard. You're wasting your time with whatever garbage tutorial you're following.