What is the difference between JControllerForm and JControllerAdmin in joomla component?
In simplest terms both are subcontrollers for JControllerLegacy.
JControllerAdmin is essentially the controller for tasks such as displaying a list of records from the database.
JControllerForm is the controller for tasks that act upon data being edited for database entry.
Here is a link to the Joomla Docs that sums it up pretty well JController Overview