There is no Host or Play button on the master server. All of that is done by the 'Create Game' button from the main menu, then making sure Public Sever is set to Yes and the appropriate settings have been made to your router (port forwarding, as well as Firewall rules).
As long as your machine has an internet connection it should be able to host a game. I think this post
goes over the basics of it all.
Most people try to organize games in the Discord
these days. Not many check the forum all that often.