Unlike most voice command apps, this app uses the microphone of your Bluetooth headset for voice input and not your phone microphone. It was designed especially for motorcycle communication, where your phone is unreachable in your jacket and you can neither see/touch the display nor use the phone mic to say your voice commands.
The app is currently in beta version, which means that there will be bugs and issues when using it. So far, I could only test it with my Nexus 4 & 5 and the Sena SMH10R headset for motorcycles helmets.
The app reads out the contacts, marked as favorites in the contacts app. When you then say the corresponding number, the "main number" of that contact is called (if no number has set to the type "main", then the first available one is selected). To add or remove contacts from the list, just star or unstar them in the contacts application.
There is no launcher icon of the app, you need to start it using the "Voice command" button on your headset. If your headset doesn't have such a button, then there is no point in using this app.