Actions in QTP provide a way to divide test scripts into logical units. There are different types of actions, including reusable actions that can be called from multiple tests, non-reusable actions that can only be called once within a test, internal actions stored within a test case, and external actions stored in another test case that must be reusable. Actions function similarly to functions but are implemented differently in QTP and allow test cases to be structured as a series of action calls.