Mendix has a large amount of learning paths about microflows. I'd recommend starting there and completing a few learning paths.
Here are some of the learning paths you could possibly try:
Otherwise you can read the documentation Mendix provides on Microflows, which contains some helpful information and tips: https://docs.mendix.com/refguide/microflows/
The best method for learning Microflow is to study the documentation and put it into practice.The only way to learn quickly is to practice.