i'm working to create an elearning course with courselab 2.4.at the end of the course i have 3 questions , my question is can i insert complete/incomplete message at the end of the test based on the result??????

As long as you set OBJECTIVES (found in the drop down menu Module.. Runtime Settings) to match what you want set for success or failure.
The help files do cover this quite well.

As you have set an objective it will have a name which is a variable so you can use it either by a javascript action or using the prebuilt actions.
So assuming you have this objective and you want a last page to say if it is complete or not.....
One method is ->
Your objective should contain a score which equals success.
Make a final page with two text objects one called fail and the other pass both with appropriate info for the user.
At the page level hide both of these using afterdisplay/display actions.
Then add below this an Ifscore action to check what the users score is and set it at your pass level. So it will check if the variable for thae objective = a pass
Then indent a space for a display action to show the pass text
Then add an else action
Next line indents a space then has a display action to show the fail text.
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There are a few other ways to do this kind of thing but this is relatively simple.