To unlock a door, swipe right on the key to reveal the Unlock button. Press the button and - Ta Da! - the door opens. Simple as that.
For your app to work, both your phone (either through mobile or WiFi network) and your device (through your home WiFi or 4G) need to be online. If either are offline, you won’t be able to use your app to open door/s.
If your phone is offline your app will have a red strip on the top letting you know.