Can't find info about pro sites

Hey wpmudev, how are you? I have an issue.

I installed the pro sites plugin, configured following this tutorial :

https://premium.wpmudev.org/blog/pro-sites-premium-upgrades/

Everything great. But now I don't get how to move foward. Where do I design my page where users would be able to sign up? Should I use a domain for that?

I have been looking for tutorials for the whole process, but I couldn't find. I would love you guys can show me the walkthrough.

Thanks a lot!