Domain Mapper issue

Hi there

Couple questions about the doman mapper please as I am still having some issues

1. Do I need to park the domains on top of teh main daomain the multisite is installed on?

I have setup the wildcard subdomain

2. If I just want to add a new site in the instalation but not use the domain mapping then I get an problem accessing the admin panel then it goes to a nothing page

but this site works as I have it domain mapped

Al ittle confuded please on the full process