Here's all you do:
1. Open app
2. Find the kind of light you have, ie, full spectrum, red/blue LED, MPH, etc.
3. Pay $5 to unlock the type of light you have, the app tells you how
4. Now you can use the app. To get an accurate reading you have to add a diffuser.
5. This is a fancy word for plain piece of white paper
6. Cut a strip that will loop around the top of the phone and cover the lenses front and back and tape in place.
7. You're ready to go! Select your light, hold phone horizontal to ground at whatever level you wish to measure. You can select par, or lux to measure with as well as some others. I measure in par cuz I find it easier to process than lux.
Hope that helps.