Look at the top of the website builder for the title of the page you are on, hover over it, and select "edit"
To add a new page, click "New Page" in the bottom left. Type a name for your page. Select an existing page you would like it to copy content from. You can "clear" the body contents to get a new page with only the header and footer.
Click "apply" and you will have a new page on your website. Note that this does NOT automatically add the page to the menu.
If you would like to remove a page, click the green X next to the page name in the left pane.
To change the name of a page, select the desired page from the left pane. Type in a new name and click "apply"