The buttons in the list are disabled

Hi Experts,

I want to create a list uibb.  Have embedded the customized list in the standard form.
I have used the standard BOFU class as the feeder class /BOFU/CL_FBI_GUIBB_LIST.

Added two standard buttons FBI_CREATE and FBI_DELETE, but these both buttons are disabled.

Can you please guide me thru the same as how to enable these buttons.

Thanks.

Sanket.