Open a static page within the customize theme pages of your store and you will see the section options on the left.
Reduced width - This will reduce the width of the content on your pages, by default the content width of your theme is 1200px wide which is great for large images but hard to keep text legible. Check this option to limit pages to a more human friendly reading width.
Choose menu for the page - When selecting a menu from this dropdown this will show as a section of links within the side bar on the right of your pages.
Page sidebar title - Only used when a menu above is selected, simply allows you to add a title to that sidebar.