Help Needed with MOSS 2007 Permissions and Group Assignments

I am having trouble understanding how and where to add users to groups on my MOSS Server. I would like to add all of my Domain Users to Viewers group. Also, I would like to add a Domain Security Group to a MOSS Group for people who will add, delete, modify documents on my sites. Also, would like a domain group added to Moss with slightly lower perms as Full Admin to create and edit web pages. I want these permissions to inherit to all Sites and Sub-Sites as well. Someone please help me to understand and make this happen.