How to setup Pro Sites signup page, trials, etc ?

Thanks for the videos on how to manage basic options, but is there a manual with everything to setup a signup page, a page to subscribe to a free trial (I don’t want the free subscription and put 15 days free trial in the settings) ?

When I get to the page I have the following message : “You must first login before you can choose a site to upgrade:”

But there is no link to create an account / signup.