We can form negatives very simply by adding NOT after the Auxiliaries in the sentences.
I am tired. I am not tired.
He is a good friend. He is not a good friend.
She was yelling at me. She was not yelling at me.
The children were playing in the pool. The children were not playing in the pool.
Birds are flying in the sky. Birds are not flying in the sky.
I may come late. I may not come late.
She might be shocked. She might not be shocked.
He has left. He has not left.
I had gone to the doctor. I had not gone to the doctor.
We have done the project. We have not done the project.
She can phone you. She cannot phone you.
I could play chess. I could not play chess.
In the following sentences we need to add DO / DOES / DID along with NOT to form negatives.
He likes chess. He does not like chess.
I come on time. I do not come on time.
He listens to music. He does not listen to music.
I spoke to him. I did not speak to him.
He broke my pen. He did not break my pen.
We drive slowly. We do not drive slowly.