Please DO NOT
use bossy language. We are here to help each other but at the same time we are NOT bound
to help. Please be professional.
Always when you post your questions, tell us what you have tried so far, be it google or anything else
I hope you understand my point.
Anyways, here is what you need.
(or SetUID) is the executable which runs with the ownership of the program owner.
That is, if you own an executable, and another person issues the executable, then it runs with your permission and not his. The default is that a program runs with the ownership of the person executing the binary.
[root@server1 ~]# ls -l /usr/bin/passwd
-rwsr-xr-x 1 root root 22960 Jul 17 2006 /usr/bin/passwd
denotes SUID, now this executable is owned by root but still you can use (when you change your passwords) it with root's ownership.
Try changing the permission of the file as root by
chmod 0755 /usr/bin/passwd
Now, login to another user other than root and try changing the password. You won't be able to do it.
Then, set SUID
chmod 4755 /usr/bin/passwd
and login to another user other than root and try changing the password. Now, you would be able to change the password.
Hope this helps. Get back if you still need help.