Drupal 8's routing system works with the Symfony HTTP Kernel. To do basic route operations, you don't need to learn very much about the Symfony HTTP Kernel.
Routing system in Drupal 8 is introduced by replacing the routing parts of hook_menu() in Drupal 7, and its parts, used for creating tabs, menu entries, contextual links, access arguments and actions are taken over by other sub-systems of YAML files (.yml) that provide metadata about each item and its corresponding PHP classes that serves the underlying logic.