Kint is part of the new part of the Devel module in Drupal 8.

Developers who worked with Drupal 7 may remember Krumo, which is a very helpful debugging tool. Kint is an almost direct replacement for Krumo.

In this video from our Drupal 8 Theming class, Rod shows you how to use Kint to print the arrays on your site.

If you place {{ kint () }} into your theme's page.html.twig file, you'll be able dig into your site's arrays and variables.