Reusable Action is peice of code that perform an action on

the application , which has application logic.

On the other hand , Functions does not have the application

logic . It performs a specific action on the data retrieved

from the application and returns the result to the calling

action.

For Ex: Your application has TextBox and Button,

Input : In the textbox we need to enter a numeric value

say 5.

Action : Calculate the Factorial

Expected : Factorial value should be displayed in the

textbox.

Here setting a value to textbox , performing the click

operation and corresponding verification is maintained in

the Action , calculation of the factorial value to arrive

at the expected output we use a Function.

Both Actions and Functions are used to access a peace of 
code, that is frequetly used.

The main difference is :
Functions have only application logic, means that we dont 
have access to the resources of a test.
For ex: we need to write a script to access Object 
Repository, Data Table etc....

Actions also have application logic and the resources 
associated with that action.

For Ex:
Say if you want to call a function, here you need to pass 
function name and all other resources like(OR, Data Table 
etc...).
Where as if you call an action, all these resources come 
with action(based on the type of the action).

1. Actions can take any no of inputs and it gives any no of 
output also, but functions can take any no of inputs but it 
will gives only one out put
2.