To begin with, the editing interface is relatively clean, however, some affordances are not obvious to the user immediately.
After site creation, the main toolbar shows tool icons that allow the user to edit site content.
The toolbar disappears while editing page content, replaced with standard save/cancel icons.
To add content, there is a lefthand sidebar. Content can be dragged from this bar to the page.
One of the options is "styled image". As you can see below, I've resized and created a circular window on an image of a leaf from Wikimedia Commons.
Adding the image is slightly tricky, as there are multiple separate areas that have options for editing. The url can be input in the window above, but also in the styled image settings below. The scrollbar doesn't reach the styled image settings, so you need to collapse the "Add Content" menu in order to reach it.
After collapsing the "Add Content" area, you can see the "Styled Image Settings"
There are three tabs for Styled image: Layout, Configure, and Advanced. The "Configure" tab has the url and alt text information for the image (arguably the most important). The default tab is "Layout". For the leaf, these settings were left as default.
The Advanced tab will not be manually changed by most users.