How do you teach a dog to spit out something in his mouth?

[Nick Willis]

For example If your dog chews something he shouldent how would you train him to learn to spit that out.

I want to know all these things because I want to be the exceptional good dog owner where I live and read and find out how to actually take care of a dog before having it so does anyone know how this 'spitting out something' can be done


And I watched this really good trick earlier on youtube and someone told their dog to freeze and it did, You could see it breathing but it had frozen on the sport whilst standing up as well how can dogs even learn to do things like this and can dogs be trained or taught a word that tells them to be gentle around small children and older people.