What sitelinks mean
Sitelinks, the term Google also uses in its English documentation, appear beneath the main result for a website and work as shortcuts to relevant pages on the same domain. Google shows them above all when search intent is navigational, that is, when someone types a brand or domain name and expects to land on a specific section rather than the home page.
They are worth separating from other elements that occupy the same area of the SERP. Breadcrumbs show the hierarchical path of a single URL and replace the address line, whereas here we are talking about several different URLs grouped under one result. Rich results depend on structured data declared by the publisher; in this case no markup activates them. The knowledge panel is a separate box that can sit alongside them on the same screen.
Two presentations show up in practice. For brand queries, Google may unfold a block of several links with a title and, at times, a short description. For informational queries it usually shows a compact row of two to four links under the result, without descriptions and with far less space. This second variant is the more frequent one and does not require the site to be a well-known brand.