A negative sentence states something is not true. A negative sentence can be formed when "don't" or "doesn't" is added to the sentence, with the exception of to be and modal verbs.
The most common negative structure is the conjugation of the verb in the negative. The structure of the sentence is usually the subject + auxiliary verb + not + main verb + objects. A common mistake in English is when the sentence contains double negatives. A double negative is the use of two "no words" in the same sentence. To modify this, use either a "no" or "any" word in the sentence.