Starbases: How do they work?

So I'm getting Sins and Sins: Entrenchment in a week and I was just wondering: how exactly do starbases work?  I know you can upgrade them but I thought that was on the tech tree.  I keep hearing people talking about upgrading individual starbases so I don't know.  Also, people made it seem like you could build ships from starbases with the right upgrade.  I would appreciate any help you guys could give me and I'll see you online.