What is the Pro sites free site creation URL or link

Let's say i want to offer free sites and have a free site button on my home page, similar to the green button on Edublogs.org.

Is there a standalone free site registration process i can use to get users in the system with a free blog, like the edublog.org/#join-network url?

is this perhaps a setting change i need to make to access this functionality. I wan't it to work like edublog.
appreciate the help.

kindest regards,