In the simple present you often negate a sentence by adding do + not or does + not.
Instead of ´do not´, you often write don't.
Instead of ´does not´, you often write doesn't.
After do not/don't or does not/doesn't the infinitive always follows.
A negation can be made with a form of the verb to be + not.
Again you can use the contraction of to be + not.
A negated sentence can also be made with one of the other auxiliary verbs + not/n't.