Making sentences negative in French is a bit different than in English, due to the two-part negative adverb and the sometimes difficult issue of placement. Normally, ne... pas is the first negative adverb that we learn. But there are actually many negative adverbs used just like it, so once you understand ne... pas, you can make just about any sentence negative.
To make a sentence or question negative, place ne in front of the conjugated verb and pas (or one of the other negative adverbs) after it. Ne... pas translates roughly as "not."
Je suis riche - Je ne suis pas riche.
I'm rich - I'm not rich.
Êtes-vous fatigué ? - N'êtes-vous pas fatigué ?
Are you tired? - Aren't you tired?
In compound verbs and dual-verb constructions, the negative adverbs surround the conjugated verb (except for nulle part [see page 2], which follows the main verb).
Je n'ai pas étudié.
I didn't study.
Nous n'aurions pas su.
We wouldn't have known.
Il ne sera pas arrivé.
He won't have arrived.
Tu n'avais pas parlé ?
You hadn't talked?
Il ne veut pas skier.
He doesn't want to ski.
Je ne peux pas y aller.
I can't go.
When there is an indefinite article or partitive article in a negative construction, the article changes to de, meaning "(not) any" (learn more):
J'ai une pomme > Je n'ai pas de pomme.
I have an apple > I don't have any apples.
In informal spoken French, ne is often dropped:
Je ne sais pas > Je sais pas.
I don't know.
And there are other uses of pas without ne.