As you create Layouts, they populate the Layout Builder page. At the top of each Layout, you can rename it, you can click on the cog icon to set conditions for the Layout, and you can delete the Layout by clicking on the Bin Icon. You can also click on the bottom of all Layouts except the Global Layout, to see and assign conditions.
Within each Layout, you can see the four Layout Section that can be assigned to each Layout. When you mouse over each Layout Section, you will see a plus icon which enables you to assign a Layout Section to that area of the Layout. You can either assign an already existing Layout Section here, or you can create a new section as well.