Build, edit and publish your site, and point your own domain at it.
Everything you can change sits on one board. Open Websites, press Manage, and look under "Make a change" for a door per kind of change.
Every page is a stack of sections, and each one changes on its own. Open the page, find the section, change it — then publish.
Publishing lives inside the page you're editing, not on the Websites screen. Open the page, change it, press Save, then Publish.
Your site already has a working address, so nothing is broken while you decide. For your own: Websites, Manage, then Domain and SSL.
You can't re-open them — our fault, not yours. Remove the domain with its three-dot button and add it again: that shows a fresh set.
Separate pages. Your site is a set of them, each edited on its own. Open Websites and press Manage to see the whole thing on one board.
No single right size — a picture is cropped differently on a phone and on a computer. Send something big with the subject near the middle.