How to create a new tab like Friends, Mine, All

I would like to know how to create a new tab in the riverdash board like All, Friends, Mine. The new tab has to include the latest discussions from all group.

Can anyone help me in doing this.

to create a new tab i have to add few coding in index.php and views/default/page_elements/nav.php.

to get the latest discussion from group what should be the code?

thank you very much for your help.