@Medic97
You are probably talking about Windy, the weather app, not Windy Maps which is a navigation app.
There is no general tutorial for Windy.
I don’t know if it can help you, but you may have a look at
http://www.maccinfo.com/Introduction_to_Windy.html
This manual is not "official" and may not be complete. Then the layout of the screen has been changed since this info has been made in 2018 by Colin a Windy user.
Concerning « how to read the colors », you have a color scale at bottom right corner of you screen (or bottom of screen for the phone app) which gives the "meaning" of the colors.
Capture d’écran 2020-09-07 à 09.43.27.png
Quite easy, no? Then for a more precise reading of wind speed you can click a point of the map to show the weather picker.