A negative sentence is a sentence that states that something is in the false. A negative sentence usually use a helping verb + not and the main verb.
Some helping verbs are is, do, does, did, was, were, can, has, have, and had.
Most times we use “do” and “does” to help make a negative sentence.
I /you/ we /they do
he/ she /it does
We can change an affirmative sentence into a negative sentence.
Affirmative sentence: John got all his sums right.
Negative sentence: John did not get all his sums right.
Sometimes a contraction of the auxiliary verb and not is used in informal speech.
John didn’t get all his sums right.