How to set up devices for VS Code for a Flutter emulator

I'd like to use VS Code as my editor for Flutter development, but I don't know how to get the emulator going. I've installed VS Code on Ubuntu 17.10.

I followed the first half of instructions as outlined on the Flutter: Get Started page (Create new app). Then I ran into trouble in the second half:

Run the app

1. Make sure a target device is selected in the lower, right-hand corner of VS Code
2. Press the F5 button on the keyboard, or invoke Debug>Start Debugging
3. Wait for the app to launch
4. If everything works, after the app has been built, you should see your starter app on your device or simulator:

The problem is that in that bottom right-hand corner is "No Devices."

How do I connect a device? I can't seem to find instructions anywhere.