Flatiron dynamically and intelligently reyour galleries based on the size of the browser window. By default, the first image in a gallery will be used as its thumbnail, but you can override that by uploading an image to Thumbnail Image in that gallery's Page Settings. When you click on a thumbnail, the images in a project are displayed vertically, and the thumbnails of all your projects are at the bottom of the page.
The Index Page consists of a series of galleries. All galleries filed under Index will be displayed in the dynamic grid-style layout described above, rather than as individual gallery pages.
You can set the size of the gallery thumbnails with the Project Width setting under Size & Values in the Style Editor. Note that this is a maximum width, and not absolute, as it changes as with the browser window width. You can also set whether or not they're cropped to squares with the Project Squares setting under Options.
Other controls for the thumbnails include:
In the project detail view, you can set the width of the page with Project Detail Width and the width of the description in the left sidebar with Project Meta Width, both under Sizes & Values.
If you connect your social accounts (do this in the backend under Settings > Social Accounts > + Add Account), the links will appear as icons under the main site navigation. The size, color, and style of these are editable in the Style Editor under Social Icon Size, Social Icon Color, and Social Icon Style.
Flatiron works best with a fairly large number of galleries in the Index. To create this, add a new gallery page under the index section rather than the main navigation. Galleries that are added as pages will appear differently to galleries under the index.
One-off gallery pages, blog pages, links, folders, and empty pages can all be added to the main navigation. These pages will appear in the main navigation in the left of the Header.