What are Custom Models and Custom Fields for?

I would like to ask what are the possible uses of the custom models and fields in the app builder. I can’t seem to find a detailed documentation or example for the uses of these functions. And if there is, could anyone guide me to a link? Thank you!

Hi, you can take a look here https://docs.axelor.com/adk/5.4/dev-guide/models/custom-fields.html