Ghost Kit has pre-made templates, so you can get started with it and build your pages quickly https://ghostkit.io/templates/
Add custom templates in theme
You can add templates in your theme, so users will be able to insert it on pages with a single click. This is a simple example of theme templates structure, that should be placed in
content.php file content:
thumbnail.png is not required, but strongly recommended, because users will see what template will look like after insertion.