Hii
Screen Exit is nothing but enhancing the screen like creating some more fields, subscreen and so on.
1. Go to the screen>System>Status-->Program (Double
click this program. It will take you to the program.
2. Now, Goto-->Object Directory Entry.
3. Make a note the package name.
4. Now run the transactions SMOD, press F4 and enter the
above noted package, press enter.
5. It will display list of Exits.
6. Now go back to the initial screen SMOD.
7. Specify the exit name here and select the radio button
Components.
8. It will display four group boxes one for FM, second
for Fcodes, thrid for Screen areas and last for
includes.
9. Goto transaction CMOD, create a new project, and
click the button "Enhancement assignments" and
specify your enhancements that you got in SMOD.
10. Now bouble clikc the enhancement, it will take you to editor with some includes starting with Z, double clikc the include you want to edit and proceed.
Refer
http://wiki.ittoolbox.com/index.php/HOWTO:Implement_a_screen_exit_to_a_standard_SAP_transaction
Regards
