how to remote shutdown a pc on my network using Terminal?

If your managing a network of Macs then you might want to consider getting Apple Remote Desktop - see https://www.apple.com/uk/remotedesktop/

This will amongst many other things allow remote control of Macs across the network - just like Windows can, it will also allow a easier way to tell remote Macs to reboot or shutdown.

Note: If a Mac is crashed or semi-crashed then often it will not be able to accept the command to reboot.

I think I may have misunderstood your question. I thought you were asking how to shut down a Mac remotely from a Mac. If you're asking how to shut down a Windows system from a Mac, I have no idea. That's beyond the scope of this site.

If you are trying to shutdown Windows machine from a Mac,

get Microsoft Remote Desktop for Mac. Once installed, simply

log into the desired machine as admin and do your thing.

The other direction should work via ssh connection. You will need to go to

Preferences->Sharing and enable remote login. You can set for all administrators

to access or specific users only.

You would have to enable Remote Login to an administrator account and then do something like this:

ssh admin@host

sudo shutdown now

That means you haven't set up remote login, or it isn't working. It's not enabled by default.