Hi,
I would recommend you to refer following docs for better understanding from scratch :
https://docs.mendix.com/refguide/microflows
https://docs.mendix.com/howto/monitoring-troubleshooting/debug-microflows
I suggest you start with the Rapid developer learning path, to understand how the Mendix domain model and microflows work.
The learning path can be found here: https://academy.mendix.com/link/path/31/Become-a-Rapid-Developer