Hi Sanjana,
Webdynpro abap is used to create web based applications by using ECC, R/3 data as backend. There are several standard components which can be reused in our components like, for Select Options in ABAP we have keyword SELECT-OPTIONS but for webdynpro, we need to reuse an standard component WDR_SELECT_OPTIONS. For ALV we have SALV_WD_TABLE. Below link will help you to understand reusability in abap webdynpro:
Also, have a look at this:
http://scn.sap.com/docs/DOC-52017
I hope this helps you
Regards,
Shahir Mirza