The links shown below some sites in Google's search results, called sitelinks (pictured below), are meant to help users navigate the site. Google analyse the link structure of the web site to find shortcuts that allow users to quickly find the information they're looking for.

Google selects sitelinks for results when we think they'll be useful to the user. If the structure of your site doesn't allow Google's algorithms to find good sitelinks, or they don't consider that sitelinks are relevant for the user's query, they won't be shown. Sitelinks are completely automated.