Sitelinks are displayed under a search result when Google thinks it might be relevant for the user, with the purpose of making navigation easier and finding the information you need faster. These are additional pages from the website, such as a pricing page, product page, blog or help sections. In order for these to be shown, the website has to have a proper sitemap that Google can crawl. These can take up to five organic positions and can generate a higher click-through-rate.
Google results on Desktop
Google results on Mobile