If I started yelling at you right now, you might get scared, or mad. You might duck down, run away, or start yelling back at me.
The way I talk, and the way you talk, to people, or to animals, really affects them, and us. Buddha told us to look at the way that we cause things. What do we cause when we lie, or yell at someone, or say mean things, or talk about other people behind their backs? We cause trouble and confusion, and hurt feelings. How we talk is one of the most important things we can look at, be aware of.
All we want to do in our life is to help people, and cause more love and positively in the world. We can do that every day, in every way, with how we talk. Buddha called that Right or Wise Speech.