Hi Mohsin,
Module pool programs are also called dialog programs and they are created in abap development work bench (TCODE: SE80).
The module Pool are reports prepared for different screens and to manage the sequence of events of these screens, in the transaction SE80 we can see all the dynpros for this kind of report, add new ones, add all types of element to the report.
The aim of the new SAP programming model is to replace long, nested screen sequences with so-called 'single-screen transactions'.
The main advantage is that it will improve the usability of the R/3 System. The transactions will be much simpler for users to use.
Input screen and data screen are combined in one window. This saves the user unnecessary navigation and ensures the correct business context.
Provide the user with the program session that best fits his or her authorizations.
Allow the user to directly access the objects to be edited. Limit the selection area using a filter, a tree structure, or for example the last edited object.
After saving the data to the database, display the edited object again. This allows the user to check the changes he has made.
Process Before Output is the part of the dynpro code that is processed before the user can do anything with the data in the screen
Process After Input is the part of the dynpro code that is processed after the interaction with the user.
Check this link for INTRODUCITON TO SCREEN PROGRAMMING
http://abapprogramming.blogspot.com/2007/08/lesson-38-introduction-for-screen.html
Hope this helps.
Thanks,
Jenny