Add user to AD group and run script

Are you looking for this to happen if they are added to ANY 3 of the 19?

Yes, the user can be added in any one group or multiple group from the list of 19 groups

I am new with the tool, can you please share your idea on how can I approach this?

Right - but you specifically mentioned "3".  Does the user have to be added to 3 of the 19 groups or simply any ONE of the 19 groups?

user can be memberOf 1 or multiple groups from those 19. say if there are GROUP01....GROUP19. the user can be member of GROUP1 only or GROUP1+GROUP2 or GROUP1+GROUP2+Group15 and so on

If all you want to do is have Active Roles react to the addition of a member to one of your 19 groups, I would proceed as follows:

1) Create a Change Workflow for the object class group and the "Add Member" action.

2) At the very bottom of the filtering conditions dialog, you can add a condition that looks at the target object name - this is where you can add an "OR" entry for each of your 19 groups.  So: Target object name is Group 1 OR Target object name is Group 2 OR Target object name is Group 3 ...and so on,

Give this a try and please post additional questions should you run into problems.

Sorry... didn't finish my thought above.

Once you have the filtering condition setup, you can add a script activity to your workflow.

Basically, you take the Powershell code that you want to run when the group membership change happens and enclose it in a function.  The function can be called anything you want.  You will need at least one parameter for your function and that is "$Request".  $Request is the object that contains that current Active Roles transaction.  There was fairly recently a thread here that talked about dealing with group membership transactions.  I posted some code in that discussion.  Suggest you have a look at this.