Site Based

Hello i am using windows server 2008.

I have 3 sites and each site is having (Domain Controller + DHCP server). and in each Site i have more than 50 VLANs

I have not configured any sites in Active Directory Sites and Services.
Everything is on default site as i can see my 3 Domain Controllers. i want to created sites so that authentication happens on site based.

I just need to create sites and move the domain controllers to that site and i need to creates subnets and assign to the sites.
anything else i need to configure.