Very Confused - ProSite Installed, But No "Signup" Page Found(Not the Pro page)

Ok, I've watched the tutorials, read several posts here, but I must be missing something here. Here's my issue:

I've installed WPMU & the ProSites plugin. After watching the tutorials and reading several posts here, I now understand that Pro is only for subscribed members to upgrade. However, where I am running into issues is the initial registration process:

Q: In my cPanel, I do see the wp-signup.php page, but WHERE and HOW does someone get to that when they visit my site?

From what I understand, the sign-up(registration) page is wp-signup.php, but when I go to my wp-signup.php page, I get a blank page.