Install Android Studio
Grab the free Android Studio software from the Android developer site and install it. The documentation is very thorough, and although there's a lot information on their site that I didn't understand or need, there were also very useful and beginner-accessible pages on getting an up running.
I upgraded my device to Android 5.1 before beginning this project, and the proper SDK (Rev 22) wasn't automatically included in my Android Studio install, so I had to use the SDK manager to install it. I knew to try that because of a very detailed error message that appeared when I tried to open the HomeMirror project in Android Studio, saying it couldn't find android-22 and provided a link to open the SDK manager:
Get a Forecast.io key
This requires you to sign up for an account on The Dark Sky Forecast site. Once you do, look for the API Key block at the bottom of developer.forecast.io. That long string of text is your unique key (I've shown you my old one for the sake of this guide, but have since reset it so the code shown is inactive).
Create an XML file with your Forecast.io key and change the text "your-key-here" for your key:
Or just download this keys.xml file, open it in your favorite text editor and make the change to include your key before moving/saving it in HomeMirror/app/src/main/res/values.
Once you have the correct SDK for the version of Android your device is running, you should be able to open the HomeMirror project in Android Studio.
Before you can run an app build in Android Studio, you need to enable developer options on your device. In your Settings > About Tablet (or Phone), tap the Build Number seven times to enable Developer Options. Then you'll be able to turn on USB debugging. More info about preparing devices can be found on this Android Developer page.
With the device plugged in, click the small play button in the toolbar to run the app.
A window should pop up asking you to choose a device, and you should see your device in the list.
The app should launch on the phone. In the setup screen you can choose various options to display and include your location. For me, errors appeared on the computer screen letting me know the face detection module was not working-- I still can't seem to get that part to work but all the other modules seem to file right up!