There are 2 different types of layouts. Pre-built layouts and Empty layouts.
Prebuilt layouts are prearranged blocks of content for specific use cases. These can be dropped into existing sections and will have the same style (background color, font color, etc) as its current section.
Empty Layouts (i.e. Placeholders)
Simply put, empty layouts are placeholders for where you can drop in blocks. You can choose between 3 column, 2 column, basic (1 column), and grid layouts. Take a look at the mockups for each layout type to see how they would look on desktop and mobile.