To create a section first click create section (nested in the blue actions drop-down). You can then select settings such as the status, SEO settings and more.
Select a page layout (this should usually be Build > Branded > UoC).
You can then choose which content types can be used from the content-types tab. If you are using a page layout that starts with "Build", you should only enable the content types that start with "Build".
Once you have your settings defined hit the blue save button.
You'll be redirected back to the homepage but can go back to start editing your section.