Footer is a block at the bottom of a web page. It is visible on all pages of your website and usually contains copyright information, name of the web design studio, contacts, etc. Sometimes menu items are duplicated in the footer.
To create a footer, go to Site Settings → Create new page. Design your footer out of one or several blocks. Save.
Then go to Site Settings → Header and Footer → Set Footer. Select the page as a footer.
Re-publish all pages.
Note. The footer won't become visible if you publish only the page assigned as a Footer. Make sure you publish all pages.
Learn more about header and footer: http://help.tilda.ws/header-footer