Install additional functionality and styles with addon 'modules' and 'themes', contributed by members like you, and free here at drupal.org
These are the instructions for finding and evaluating contrib modules to use on your site.
Describes the process for adding a module to your site
Composer is the PHP package manager. It provides features similar to Drupal's own dependency management, and Drush make, but for any project
Instructions for installing a modules using drush or drupal console
These are the instructions for installing themes on Drupal 8
Describes how to update a module to its latest version
Some modules require post-installation configuration. This describes generally how to do that.
Describes the process for finding the documentation related to any modules you may be installing
Describes how to remove modules from your system when they are no longer needed
Instructions for installing a sandbox module on Drupal 8
Describes common issues in module or theme installation and how to solve them