Issue with github deploying

Hi folks, I trying deploy my Hugo site and I use Hugo Docs instruction: https://gohugo.io/hosting-and-deployment/hosting-on-github/#step-by-step-instructions. There is example on Step-by-step Instructions (paragraph 6): git submodule add -b master git@github.com:<USERNAME>/<USERNAME>.github.io.git public
That made confuse me. What do I need insert USERNAME>/<USERNAME?
I’v attempt put: git submodule add -b master git@github.com:cosmos-factory/test.github.io.github.io.git public
but then I obtain: fatal: repository ‘cosmos-factory/test.github.io’ does not exist.
I have repository: http://cosmos-factory/test.github.io

You should fill the <USERNAME>/<USERNAME> with your Github username.

For example:

git submodule add -b master git@github.com:ardianta/ardianta.github.io.git public

Where ardianta is my Github username.

No, it doesn’t work

Have you create the <username>.github.io repo on Github?