I am going to start describe few new things in Drupal 8 in easy way.
Now in drupal 8 version uses Symfony few Components, rather than all of Symfony. If you want to check the list of use components in druapl 8. You can check in 'core/composer.json' file.
We will render/call all variables of twig file in double Curly Braces/Brackets, Syntax.. {{ write variable name here }}