Sitelinks represent the site's main page and sub-pages displayed in the Search Engine Result Pages (SERP) in a structured way, based on the users' queries and the relevant pages.
When a person types a query (a keyword or a phrase) in the search engine to get information about the searched topic and discover pages, they face Google's search results, called sitelinks. They are displayed in the SERP in a structured way (based on the site's structure), and their role is to help users navigate through sites, using shortcuts that will save users time and allow them to find the information they're looking for quickly.
Google's algorithms automate the shown sitelinks based on what is considered useful and relevant to the users' queries on the search engine.
Moreover, in order to get automated sitelinks, make sure to have a structure of the site that will allow the algorithms to find good sitelinks; otherwise, no sitelinks will be displayed no matter the users' queries.
Amongst the best practices to follow, to improve the quality of the sitelinks, Google recommends to: