Function:- function is a group of methods and instruction 
and it can be access whenever we call that function 

Action:- action is use to split our test script into more 
flexible and logical unit advantage:- 1.if we require a 
particular step of our test script then we can use action 
by making it reusable action. 2. if 2 or more than two 
scripts require the same script then we go for the action

Action -> Action is nothing but a script written for certain
function point .
Action types ; Non-reusable , reusable , external
Action may return multiple values .
Action requires its own object repository( requires objects)
Actions concept i restricted to QTP only ..

Function -> it consists of Set of statements written to
achieve a particular task.
Function returns one value.
Functions concept is used all programming
languages,scripting languages.

Types of functions in QTP->Built in ,Local Script,Library
functions.
WIthout using objects Functions can be written ( in
descriptive programming )

the difference between action and function is
action has object repository.
function doesnot have object repository.
we can edit copy of actions.it may not effect on main action
we cannot edit the copy of function. it my effect on main 
function.

diffrence is Function can return only single value whereas 
Action can return multiple values.

Action will have object Repositery associated with it
Function will not have .
Function has only one return value 
Action can have many return values
A function can be external declared and called from 
liberary files.
Action cant.

any Query contact : prataphs@gmail.com

1.FUNCTION WILL RETURN ONLY SINGLE VALUE BUT ACTION CAN    
RETURN MORE THAN ONE VALUE.
2.ACTIONS CAN USE IN OTHER ACTION AS FUNCTIONS BUT WHEN WE 
COPY THE ACTION IN OTHER ACTION AND EDIT THAT ACTION ...iT 
WILL EFFECT THE MAIN FUNCTION BUT FUNCTION CANT.
3. ACTION IS OBJECT REPOSITORY ABUT FUNCTION DONY

Actions can Return  mutiple values, where as function will 
return one value 
Check points insertion wont be possible in functions where 
it can be possible in Actions . 
functions can be called outside the tool , where as Actios 
are called only within QTP 
scripts written in higher version of qtp wont be compatable 
with Actions , where as functions since they are not QTP 
related can be work in any version 

functions can be even written in notepad , wiht .vbs file 
name 

ex : 

Public Function F1 
msgbox(" I am function")
end function 
call F1

run the code in notepad and verify

Action- Action is nothing but a step performed by user.
Action is catagorized in two parts
Reusable action,usable action.

Function-In that action what functionality u r written to 
check that function is working properly or not.
e:g - if you write a script for the login page,the total 
script is written for the login page is a action,and the 
script was written for the login page is the 
function,because main functionality in the script is login 
the page.

if it wrong reply me

1. Function is a feature of Vb Script whereas Action is specific to QTP.
2. Action is associated with object repository whereas Function is not associated with object repository
3. Function can have at maximum one output value whereas Action can have many outputs.
4. Functions is just logical instructions which are not associated with objects whereas Action is associated with objects