After you open the editor, in the centre you can see ‘Add header’ button and if you click on it, It will take you to the gallery of headers, where you can choose the one you like, the same with the ‘Add footer’ button, which is located in the centre of the page, but at the bottom. When you click on ‘Add Block’ button, which is located in the middle of the page, you will be able to fill your website with many different blocks from the gallery.
