Explain Module pools with example.

A Module Pool program is a Dialog Program (a number of screens that are linked together and use the PBO and PAI events). An Executable programis a Report which generally has a selection screen and a output screen (these types of programs use the Start of Selection, End of Selection, etc events). Also a Executable program can be run via SE38/SE80, but a module pool program must be run from a transaction code as you need to specify the starting screen. So when you are creating the transaction code, you have to first know what type of program you wrote and choose the appropriate type. If you wrote a screen based dialog program, then choose the 'Dialog program' radio button, and if created a report program, then select the second one for an executable report.

Also you can see the below examples...

Go to se38 and give demo*dynpro* and press F4.
YOu will get a list of demo module pool programs.
One more T-Code is ABAPDOCU.
YOu can find more examples there.
See the prgrams:
DEMO_DYNPRO_TABLE_CONTROL_1 Table Control with LOOP Statement
DEMO_DYNPRO_TABLE_CONTROL_2 Table Control with LOOP AT ITAB