Sections can be added to any Page, to learn more about creating Sections, see page 8 of the Theme Documentation
Using the dropdown menu, select from your already created Sections. Choose "+Add More" to add additional Sections to this page.
To rearrange the Sections, click and drag where the "|||" appears.
To remove a Section click the box with the "-" sign. If you remove all the Sections, be sure to hit "Update" so that the "+Add More" will appear again.