Starting the discovery of the PU system, I found it was not so easy to get information.
About the "Powered Up" app, I found this complete reference:
https://racingbrick.com/powered-up-code-block-guide/
*** EDIT***: full version:
https://racingbrick.com/powered-up-code-block-guide-full/
***
For the 3D sensor in the hub, I draw the following
And the following code in the app to check the 3D sensor values:
Please feel free to reply on this post, if you have valuable info for beginners.
And these basic tuto's: (in french)
http://chezyannoch.com/tuto-lego-powered-up-programmer-son-hub-et-utiliser-ses-moteurs/