To install a chosen plugin you should download and enable it. Check the example listed below:
# drush dl addtoany
Project addtoany (7.x-4.0) downloaded to sites/all/modules/addtoany. [success]
# drush en addtoany
# drush cache-clear all
# drush help archive-backup
https://www.drupal.org/node/1096994
http://orga.cat/posts/most-useful-drush-commands
https://www.siteground.com/tutorials/drupal/drush.htm