From the Workflows tab, an Account Admin can set user permissions by clicking on the ellipsis button on a stage, selecting Edit Stage, and by clicking on Select Users. Select the users you'd like to add to the stage and click Save. Once a user is added, they can move the post to the next stage. If no user is selected for a stage, it defaults to All Users.
Note: Account Admin's don't appear in the user drop-down menu because they already have full access.
If a user doesn't have permission to move a post past a certain point, they will see a "You don't have permission to update past (stage name)". The post will revert back to the last stage they have permissions for.
Enabling Users to access the Publish 3.0 Tab
This is for Account Admins. If you want a user to have access to Workflows and Publishing, make sure to turn on the "Can View Publishing" and "Can Create Posts" permissions for that specific user.