How do nonverbal communication make communication effective?

use gesture and eye contact
Using gesture makes your presentation more interesting. You might seen some teachers who just stand there and talk. You might think the sound actually comes from a speaker.
Eye contact is also important. When someone speaks to you, but looking somewhere else, you might feel that he is not respecting you.

Well, ever think of those who are unable to talk? Deaf & mute people uses sign language to communicate.

and for others, nonverbal communication skills will get attendion from listeners