Twig Extensions allow to create custom functions, filters and more to use them in your Twig templates.
The default Twig filters and functions; The Twig filters and functions added by Symfony; The official Twig extensions related to strings, HTML, Markdown, internationalization, etc.
The most common and recommended way to install the Twig on Linux Server is via Composer which is a PHP dependency management tool.
https://ibmimedia.com/blog/187/install-twig-on-linux-server
install twig without #composer
composer update twig
twig documentation
composer install twig extension
twig composer
symfony/twig-bundle
how to use #twig
twig tutorial