Thanks skaero for your immediate replies.
Actually, I'm trying to add a tab for "blacklist" in settings -> preferences section and then add the necessary controls(list, textbox , etc) to add to, delete from and display blacklist. To add those control as I understood I have to use template hooks and understand how to extend the objects given in it. This is my first experience with roundcube so I found it bit difficult to get a clear idea of how to extend those object to suit my requirements. Also I don't know the available template objects in detail. So It would be great if some one can help me on this.