Setting up server, getting "'ssh' is not recognized as an internal or external command"

I’m following the Initial Server Setup directions and am close to the end of that page. I’m now trying to connect to the new server from my local machine. The instructions say to use this command: ssh demo@SERVER_IP_ADDRESS. When I try that in a terminal window, I am told ‘ssh’ is not recognized as an internal or external command. I am using Windows and using PuTTY to connect. The instructions say if I’m using PuTTY to “be sure to update the session’s port number to match your server’s current configuration.” I have been using Port 22. I tried that again, and then a terminal opens up asking for a password for “root”. I don’t think I have a password for root because I created the droplet with an ssh key. I tried the password for my user, but that did not work. i tried connecting on port 23 not knowing if that would work, and it did not. What should I do?