Teaching commands is when you have a prompt that says "To do X, say Y".
As James Giangola, Conversation & Persona Design Lead at Google, points out in his article "Conversation Design: Speaking the Same Language"  that this is a carry over from customer service style phone trees.
Granted, the interaction model for these type of prompts end up being much simpler (you just need to include X & Y sample utterances) however from the user's perspective, it is a bad experience. It is not used in conversation between humans and is not intuitive.
-  6. Don't Teach "commands" -- speaking is intuitive - James Giangola - link