Vladimir,
You need to go to your business decision makers ( ie Supervisors, Executives ) and request that they provide you a Visio Diagram detailing the requirements of your application. If they cannot provide that for you, then I don't recommned designing the script. You can translate the steps in the Visio directly to "Labels" in your script. Once you have that it's simply a matter of figuring out what steps you need to use to impliment the call flow the way the visio is laid out.
Check out the Media sections of the website, there are sample scripts there as well as CRS Scripting Reference volume 1,2, and 3.
Alex