In your library the different parts of each reference are displayed under headings such as Author, Year, Title, Journal, etc. Click on any of these headings to change the order of your references either alphabetically or chronologically.
You can find more possibilities for sorting under top bar > Tools > Sort Library
Note the language setting: Sort orders can differ with language. In the Netherlands other sort rules apply then in say, United States.
NL: Broek, J. van den
US: van den Broek, J.