@Mondeuse Salut, There is no real guide to explain how to use this App. You can get information via this link https://community.windy.com/topic/3361/description-of-weather-overlays A member created a user guide some time ago   http://www.maccinfo.com/Introduction_to_Windy.html   But it has not been updated since that time.   If you have special questions, you can ask them here.