Drush is a computer software shell-based application used to control, manipulate, and administer Drupal websites. On the surface, drush is a tool for updating site modules, however Drush has a more comprehensive list of features.
Drush core ships with lots of useful commands for interacting with code like modules/themes/profiles.
Similarly, it runs update.php, executes sql queries and DB migrations, and misc utilities like run cron or clear cache. Drush can be extended by 3rd party commandfiles.
Follow below steps to install:
Step 1: Install Composer using this link
Step 2: Type below command to install Drush globally
$ composer global require drush/drush:8.*
replace 8 with the version you want to install.