Sorry to keep posting questions here but forum searches and help searches did not answer.

How do you control the site page hierarchy? In "Page Manager" all you can do is move pages up/down. How do you set up a parent/child page relationship?

You can't. There was a thing in RSD2.5 that allowed you to apparently place a page as the child of another page, and my guess is, that it was meant to be the start of some kind of folder structure, maybe also something that ended up as a menu structure. But in SD3 this seems to have been left.