You mention cmd so I'm guessing this is a windows machine. You need to install a program that supports ssh. Putty is a popular windows program that does.
From Putty's website:
In really simple terms: you run PuTTY on a Windows machine, and tell it to connect to (for example) a Unix machine. PuTTY opens a window. Then, anything you type into that window is sent straight to the Unix machine, and everything the Unix machine sends back is displayed in the window. So you can work on the Unix machine as if you were sitting at its console, while actually sitting somewhere else.
Putty download site
If that doesn't work check to see if a port is correctly forwarded.
Go to You Get Signal type in the ip address of the server and port 22 (the standard ssh port) and click check.