Below points explain how functions are different from actions.
Functions are not associated with Object Repository and Data Table whereas Actions maintain their own Object Repository and Data Table.
Functions are elements of VB scripting that are not only restricted to UFT whereas Actions are elements of UFT.
With the help of functions, the code gets re-used and with actions, the test gets re-used.
The common feature between functions and actions is that both are associated with input parameters, output parameters and return values.
A Script can be divided into multiple Actions like Sign In, Sign Out, etc., whereas Function is created in a script.
Action Example: Entering any value or data in any field or clicking on any button of an application is termed as an Action. (Entering 20 against the age field is termed as action or Clicking on the Submit button is also an action).
Function Example: Any calculation part or formulae behind clicking on any button is termed as a Function. (After clicking on the ADD button, the addition performed at the back-end is done by a function).