How to add a block that will appear on every page of your website
To place an element (a menu, for example) on every page of the website, create a new page, add the elements you want to appear on all pages, go to Site settings → Header and footer and set the created page as header and footer.
Header is a block that runs across the top of every web page. Typically, it contains a logo, menu, contacts, language button or a shopping cart if an online store has several pages and a shopping cart is required for the whole website.
To set a header, create a new page then add the required elements such as a menu or logo. Go to Site Settings > Header and footer and assign the page as a header.
Footer is a block at the bottom of the web page. It contains useful, but not essential, information and is visible on all pages of your website. A footer can contain copyright information, name of the web design studio and contacts. Sometimes menu items are duplicated in the footer. Set the footer just like you set the header: Create a new page, design your footer, go to Site Settings > Header and Footer and assign the page as a footer.
For your header and footer to show on your website, publish all pages (and not just the pages assigned as header and footer.)
How to remove a header or footer on a single page
To delete a header or footer on a single page, go to Page settings > Additional > Don't use header for this page / Don't use footer for this page.
Republish the page.
If you have an online store, it's a good idea to include a cart in your header or footer.