I feel it's important to state that in order to train your voice you must work with a vocal coach or professor of voice one on one. If you getting this through a tutorial without this interaction it's very easy to start and/or reinforce bad habits and even possibly do damage to your voice.

The voice course here is very basic, but what specifically do you see as a lesson that could lead to physically damaging your voice? Yes, a personal coach is best, but many people don't have access to, or can't afford one.