I am new to Pro Sites. How do I get this started (after it's installed)?

I am new to Pro Sites (and WPMU) and I don't understand, after Pro Sites is installed, how to allow users to use it, etc.??

Meaning, how do I allow a new customer, once they visit my site, to start the sign up process and select the options to create their new site? I feel a bit lost.

I've installed Pro Sites .. but now what?

I want to be able to allow people to sign up, select their choice of the available packages, select options, and even enter their domain name to be used (I guess using the Domain Mapping plugin), etc. so they can be set up automatically.

Is there any documentation that explains how to set this up, step by step, etc.??

What's the process?

I just saw (after activating the registration process) that a user can go to a "wp-signup.php" page. Can anyone tell me how and where to CUSTOMIZE this look and feel? How can I make this look different? Where can I go to make changes to the sign up page?