First time sudo and Linux

We have a linux system at all locations that is not really used interactively. Well the users need to shutdown the box on weekends. to do this they usally call us to shut it down remotely with root. well i just came accross sudo. and i am unsure how to use it
i did
visudo

then i did
%mliu ALL=/sbin/shutdown

I saved it but it said i need to be root to execute the script. did i type something wrong?

I think you should have a clear idea about sudo before using it. Please go through the URL sudo - Linux Command - Unix Command and do accordingly. If there is any issue, please feel free to discuss farther.

i got it working thanks