Add a role to the specified user accounts.
drush user-add-role
role : The name of the role to add
users : (optional) A comma delimited list of uids, user names, or email addresses.
Add the "power user" role to the accounts with name, id, or email 5 or user3, uids 2 and 3, names someguy and somegal, and email address of billgates@microsoft.com
drush user-add-role "power user" 5,user3 --uid=2,3 --name=someguy,somegal --mail=billgates@microsoft.com