Drush is a command-line shell and scripting interface for Drupal.
To install Drush, SSH in to your server as root and run the following commands:
sudo wget -O /usr/local/bin/drush http://files.drush.org/drush.phar sudo chmod 755 /usr/local/bin/drush
You can then invoke it as simply
drush
Drush has many commands and options available. For information on using Drush, see the Drush documentation.
Be sure to run Drush as the system user your app belongs to, not as root. If you invoke Drush as root, you will end up with file permission errors in your application.