When you first open up a page or post in the WordPress admin after it upgraded to Gutenberg, it looks entirely different. There is a plugin called Classic Editor that will allow you to keep the old look, but you might as well just jump in and get started with the new format.
Classic Box vs Gutenberg Block
The classic editor, currently, still has many of the old features, but not sure if those will stay around or not. If you create a new post or page, it will have “blocks”. So, now each paragraph or heading is in it’s own block, not one long box. hmmm, why? no clue, but that’s how it is.
How Do I convert the Classic Box to a Gutenberg Block?
Click inside the box and a 3 dot button will appear in the upper right corner. Click it and click the option to convert to block.