You need an adapter that plugs into the OBDII port of your Leaf and then uses either WiFi or Bluetooth to connect to your phone which is running the LeafSpy app. If you search around you will find several recommended models available on-line. Some apparently work better than others and it might matter if you are using IOS or Android so search a bit first. Or you can go to the Engineering sub-forum and I believe the author of the app is active there.