I'm currently creating a website in Google Sites "from scratch" - meaning it's a blank canvass. I started working on it using the admin access which was made by another person. Eventually I assigned edit rights to myself because all the work was being logged under the admin account, and I needed to know which ones were done by myself and which ones were not (makes it easier to troubleshoot just in case something goes wrong).
The primary problem I experienced was I could not see the "Site Layout" tab which is mentioned in this Google Sites Help page: configuring your sidebar and navigation gadget.
I learned later on that you need to have full access to the site, including the right to change the layout. Which means admin access! So I'm going back in as admin to create this part of the website. The Navigation bar is great for rearranging the page order. I'm glad I figured this out after only about a couple of hours' worth of trying to see what's wrong.