In English we can turn a positive phrase into a negative one with the use of our word not.
The "not" itself is important, but it doesn't work alone. The sentence is made negative because the verb is made negative. In our example above the verb happens to be "is".
Put the "not" anywhere else in the sentence and it won't make much sense. (Unless you're a fan of ridiculous irony... "He is here.... NOT!")
Understanding this makes it easier to understand how to form negatives in French. In order to turn a sentence negative, we need to make our verb negative. And to make a verb negative in French we simply wrap the verb in two little words: ne.... pas.
Note that when the verb begins with a vowel, ne contracts into n' and it's added to the verb, like this: