In order to run the app, you need to installed the Android Studio IDE. Follow the step-by-step guide provide by google to install the Android Studio.
With Android Studio installed, you have to run Android Studio. Go to the "File" menu and chose "Open an existing Android Studio project". Browse to the location of the project (the folder) and click open.
After all the processes are finished by Android Studio and the project is fully loaded, connect an Android device to your laptop through a USB cable and run the app.
In order to run the app, you have to press the green play button at the top of the screen and select the name of the mobile device you have connected.
If Android Studio does not recognize the device, you have to make sure your device has developer mode enabled.
At this point, the app will be already in the menu of your device, ready to run.