An anchor link is a link that, when clicked, pushes you to a dedicated section further down the page. They're great to use as a Call-to-Action in a header.
To add an anchor link, you just need to go to the block settings where you want to push people to on the page, select the "Settings" tab and add a reference in then "Row ID" field, like so:
Then on the button that you'd like a user to press and have it push them to the contact section, switch the "Button Type" to URL and add #reference (ie #contact) in the URL field, like so (be sure to include the pound sign).
Then press save.
Please know that this anchor link setup will only push a user to a block on the same page as the button.