Beginner Drush question. Can't get Drush to do anything!
There is a known problem of using Drush with DevDesktop on MacOSX.

Quick fix

Instead of running drush like this:

$ drush status


Run it like this:

$ DEVDESKTOP_DRUPAL_SETTINGS_DIR="$HOME/.acquia/DevDesktop/DrupalSettings" drush status


Permanent fix

Everything is explained in this article:
http://btmash.com/article/2015-03-24/using-dev-desktop-composer-drush

Why is it happenenig?

Acquia DevDesktop keeps all credentials in a specific folder and let PHP have access to that location via a $_SERVER variable called $_SERVER['DEVDESKTOP_DRUPAL_SETTINGS_DIR']. This variable is provided by Apache and PHP only sees it is run by Apache. But when you use Drush, PHP is called directly and that variable does not exists anymore and Drush cannot find the database credentials.