First you buy the barrel and use it to replace the one in the firearm, then download the app and sync them (the app won't work unless synced to a barrel, so ignore the bad reviews that only tried the app by itself). Syncing is very easy and the app intuitive to work. You can keep track of holster type, body location, etc and get all the draw statistics as you continue your practice. Really a great product to help improve your draw time. Highly recommend.