You can fill in meta information (information about your website) concerning a website, such as key words and a description. These have a partial influence on the ranking in the search results, but they do not in many cases. The recommendation from M&C:
Manually entering keywords is no longer necessary, search engines determine the keywords of a page on the basis of degrees, words in the URL, intermediate buttons and words that occur frequently in the text. Manually entering search terms would be very sensitive to spam: people would be able to use popular but irrelevant words to appear higher in the search results.
This is carefully explained by Google in a video on YouTube concerning the use of keywords.
Search engines use the description (one-sentence summary of what can be found on a page) regularly, but certainly not always. Google for example attempts to identify a sentence on a page that summarises the content well. Google displays the description that has been entered manually if Google is not able to find such a sentence.
Example of a description in the Google search results (bottom two lines):