Multisite User Blog Creation Issues

To Whom It May Concern-

I have set up Multisite (have access to Network Settings, Setup, etc), but when I try to add a site as a Super User, the domain (example.mydomain.com) cannot be found.

When a regular site user tries to create their own blog, they are redirected back to the main site homepage.

How do I fix these issues? I have installed the Blog & User Creator plugin and allowed complete freedom with those settings, but nothing seems to be working. I'd appreciate any assistance you could provide.

Thank you,
-Zach