Apache has long been the predominant web server, but it is by no means the only server. While Drupal was originally written with Apache in mind, many other web servers (including IIS, Lighttpd, and NGINX) can run Drupal.
We do not explicitly cover the web server layer anywhere in this book, primarily because development rarely requires working at that low level. However, Drupal expects a fair amount of processing from the web server layer, including the handling of URL rewriting. For more information on what you can expect, you can consult the relevant documentation page at https://www.drupal.org/docs/8/system-requirements/web-server.