The command “pm-download” or the alias “dl” will download a project. If you are downloading Drupal, it will download to the current directory. If you are downloading a module or theme, it will be placed in the appropriate location.
drush dl [project_name-version]
drush dl views or drush dl views-7.x-3.x-dev
Typing “drush dl views” will download the latest stable release of the module, while “drush dl views-7.x-3.x-dev” will download the latest dev version of the 3.x branch.
Technically, Drupal core is a project, so you can use this to download a fresh copy of Drupal itself.
drush dl drupal or drush dl drupal-8.x-dev
After I've downloaded Drupal core, I usually rename the folder to something that represents the site I'll be working on. In this case I'll rename the directory to "drushsite", then change directories into the Drupal root directory.
mv drupal-7.22 drushsite