Multiple page site allows larger site to better organize info.
Open the page manager on the left side menu. You can see existing pages listed there. To add a new page, click on the  Add Page  button. You can also click on the folder icon to add a folder. Different from page, folder can only be used to contain other pages.
The pages of your site is listed in the page manager. You can use the dropdown menu on the right side of each page to manage each page.
You can drag pages to re-order them or move them into sub-pages of some page or folder.
For elements that appears on every page, e.g. site menu, site footer, you can put them into the Header/Footer section of the page.
Optional. To rename a page, just double click on the page name.