WordPress MU

I wanna install subdomain in WPMU. I know how to install it in admin panel. But I wanna know how to install new Subdomain such as:
subdomain.Maindomain.com
I need install database separately in subdomain.Maindomain.com or How?
Who can explain it step by step or show me the link with explanation?!
Thanks a lot.

You set up your DNS wild card for your domain

You set up wildcards in Apache so it can support subdomains.

You install WPMU in subdomain mode

Each new blog when it is created is created as a new subdomain. Its all virtual, only one database.

Its actually explained in the instructions.