In short, nano is a command line text editor. When you ran that command, it opened a new document in nano.

Next, I’d paste the configuration info from the guide into this window.
You should see it appear in the window after pasting.

The menu at the bottom is a list of handy nano commands, the ^ signifies the control (ctrl) key, so to exit that screen you would press “ctrl+x” - it will prompt you to save it, press enter and then “Y”.

Another tip I would leave you with is how to use an SSH client on your computer to connect, like this tutorial describes for Windows users:

How To Log Into Your Droplet with PuTTY (for windows users)

If you use a Mac or Linux workstation, then SSH is built into the terminal app that comes with those operating systems.

Hope this helps and good luck!