To run the app, go to Run | Run app or click on the play button.

Android Studio will prompt us to select the deployment target, the physical device that has developer options and USB debugging enabled OR the emulator, also known as the virtual device the user has set up.

Once we select one of the options and click on Okay, the app will be built and run on the deployment target. The app will be up and running and we should see map activity being loaded with Marker in Sydney: