There are two ways to use the word "bark." The first is for the sound that a dog makes. Dogs bark. The second use of this word is for the material that covers the outside of a tree. Most trees are covered with bark.
Here are some examples of ways to use the word "bark" in a sentence:
He’s barking.
That dog won’t stop barking.
He’s barking because he’s protecting his territory.
It’s really annoying to hear a dog bark all the time.
People who own dogs need to train their dogs so that they don’t bark all the time.
His bark is worse than his bite. (This is an expression. It means that he sounds dangerous, but in reality he won’t hurt you.)
You’re barking up the wrong tree. (This is also an expression. It means that you have made a mistake in whatever it is you are trying to pursue.)
bark
The bark on this tree protects it from insects and animals.
Without the bark, the tree would die.
Some trees are valued for their beautiful bark.
Bark develops cracks and crevices as it expands with the growth of the tree.
He’s barking. 
bark