Changing Role Capability

I have read documentation but am having trouble changing the role capabilities.

Basically, all I want to do is to allow ‘Editors’ to add/manage users.

Is there more involved that simply changing wp-admin/includes/schema.php?

Also, I can understand capabilities: add_users, edit_users, delete_users, list_users, even promote_users; but what are create_users and remove_users?