We can call a function using below method.

Call Function Name("Hello World")
[public/private]Function Function(text [Arg List])
   MsgBox text [Description]
End Function

we can call the function by using tools>general 
options>folders...........
(or)
call test_name ( [ parameter1, parameter2, ... 
parametern ] );

if it is wrong plz tell the correct...........

                                 thank you

Even if U don’t specify CALL keyword & just write this way:

FunctionName (Parameter1, Parameter2,….)

This will call the required function

First u Write the test. And then rename the action (shift + 
F2) then which test u want to call that renamed function 
open the test Choose call to Existing Action. choose which 
function u wand to call the action name automatically 
appear in the action's box. And then click ok function 
called.
Rename Steps:
Edit-->Action-->Rename (or) Action Property.
Steps for Call Function:
Insert-->Call to Existing Action-->select the test from 
list--> Choose where u want call the function then press 
ok. Finally u see that test RunAction.... step appear

First of all we need to add that function into resources 
tab and script as call <function name>(arguments if any)

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