Follow these instructions to create and run your first app:

https://developer.android.com/training/basics/firstapp/creating-project.html

https://developer.android.com/training/basics/firstapp/running-app.html

If you are having trouble following along with the articles, the second half of this video (starting at 5:20) shows the process: https://www.youtube.com/watch?v=Z98hXV9GmzY.

You should now have a blank app running on either your phone or the emulator! Let's play with this a bit more.

Open activity_main.xml. To do this: you need to open the Project panel on the left. Then you need to click your way down into app > res > layout. Use the small down arrows to navigate the file structure. Double click activity_main.xml. There should be two small tabs at the bottom: Design and Text. Make sure you're on Design.

This is the visual layout editor. You can use this to drag and drop elements to build your user interface (UI). On the left, you will see a panel called Palette. It contains many of the common UI elements found in an Android app.

Go ahead and drag some of these elements onto the canvas in the middle to build your UI. You can double click on TextViews and Buttons to edit the labels on them. Use the dropdown above (it might say something like Nexus 4) to see what the UI looks like on different screen sizes.