Main drush docs are at http://docs.drush.org/
or.. http://drushcommands.com/drush-6x/archive/archive-dump
A helpful user guide: https://www.drupal.org/node/2132447
Site archive function (http://drushcommands.com/drush-6x/archive/archive-dump):
drush archive-dump --tar-options="--exclude=.git --exclude=sites/default/files"