This one is a basic question. I would suggest you to go through the QTP tutorial or attend QTP training. It will help you with other basic concepts as well.
To answer your question in short-In QTP we divide a script into reusable actions, these reusable actions can be called from other actions and thus can be used in your diff-diff scripts.
To answer your question in short-In QTP we divide a script into reusable actions, these reusable actions can be called from other actions and thus can be used in your diff-diff scripts.
Want to fast track your QTP/UFT Learning? Join our UFT Training Course