The mouth is an organ in humans and many animals. The birds also have a mouth, but one speaks of a beak, which they have instead of lips. In mammals, one speaks of the mouth or the snout. What is special about the mouth of man above all is that his lips are red.
The mouth is an opening in the head through which one feeds. In the mouth, the food is chewed and moistened. The saliva prepares it for digestion. Food and drink then enter the stomach via the esophagus. The tongue is a large muscle in the mouth.
The tongue rotates the food as it chews, constantly pushing it between the teeth. They can be used to break up food. The tongue also helps with swallowing. On the tongue are the taste buds, which are used to taste.
You can also breathe through your mouth, just like through your nose. Breathing through the nose has the advantage of making the air humid. However, the nose can be blocked, for example by a cold, then only breathing through the mouth remains. Many animals use their tongues to cool their bodies because they cannot sweat: a lot of salivae evaporates on the tongue when they breathe. This cools the tongue down.
Also, the mouth is there to make sounds. We already know this from animals that roar or hiss. This is how they threaten other animals. Of course, people also need their mouths to speak or sing. However, the tones are not created in the mouth, they are only changed there. The tones originate in the throat. The vocal cords are located in the larynx.