WordPress MU

Hai,
I was try doing some simple code for my wordpress MU.I just want to able to login form at frontend.I try do the logout part so every member can logount easily at fronend.
I was findout the logout url suppose like this:
http://subblog.example.com/wp-login.php?action=logout&_wpnonce=e65e0855cb

So,my question is what is wpnonce at the url?how to get the e65e0855cb value?

Thanks.

Regards,
Wallace

use <?php wp_loginout(); ?>

Dear Ovidiu,
Thanks a lot.......

Regards,
Wallace