I am still a bit unsure about how my network of multisites works.

I am still a bit unsure about how my network of multisites works. I have a network set up and I am super admin. I have created two sites. I would like one site to be my main site, and then allow users to create their own sites under this site. So my second site would be the example of one of the users sites.

Can someone run through how Networks work…How do i tell my network that site 1 is the main site, and all other sites are sub sites for users to be created by users.

In addition, If i were to have a create an account/site page under Site 1, what would this entail and how would users create their own sites.

Im not sure if Im getting at what I really need to know, but ive looked over several WPMU and codex things and still cant grasp this.

Thanks