To make a negative sentence in English we normally use Don't or Doesn't with all verbs EXCEPT To Be and Modal verbs (Can, might, should etc.).
Affirmative: You speak Spanish.
Negative: You don't speak Spanish.
Contractions
Don't = Do not Doesn't = Does not
I don't like fish = I do not like fish.
There is no difference in meaning though we normally use contractions in spoken English.
Word Order of Negative Sentences
The following is the word order to construct a basic negative sentence in English in the Present Tense using Don't or Doesn't.
Subject
don't/doesn't
Verb*
The Rest of the sentence
I / you / we / they
don't
have / buy
eat / like etc.
cereal for breakfast
he / she / it
doesn't
*Verb: The verb that goes here is the base form of the infinitive = The infinitive without TO before the verb. Instead of the infinitive To have it is just the have part.
Remember that the infinitive is the verb before it is conjugated (changed) and it begins with TO. For example: to have, to eat, to go, to live, to speak etc.
Examples of Negative Sentences with Don't and Doesn't: