Sitelink extensions appear at the bottom of a Text Ad and link to a different part of the website than the landing page, thereby extending the Text Ad.
They are used to give users a link to a part of the website that may also be relevant or related to their search but not directly in the keywords that were searched, to provide information about some of the other services or products offered, and to give the user information on the advertiser (such as a “Contact Us” page, for example).
They often link to sections of the website that provide a better experience for the customer, such as directions, a map, or other product categories (and in the example below, different locations).
They should look similar to this:
Source: About sitelink extensions