Negation

German has two ways to say no, and choosing between them is mostly mechanical once you see what is being negated.

Negating a noun that has ein or no article at all → kein. Everything else → nicht.

• Ich arbeite heute nicht.

  I am not working today.

  negates the verb

• Ich habe keine Zeit.

  I have no time.

  Zeit has no article → kein

• Das ist nicht mein Auto.

  That is not my car.

  mein is a possessive → nicht

• Ich trinke keinen Kaffee.

  I do not drink coffee.

  accusative masculine → keinen

• Ich kann heute nicht arbeiten.

  I cannot work today.

kein takes exactly the same endings as ein — which is convenient, because you already have to learn those.

Where does nicht go? Late — but in front of whatever it negates. Before an infinitive (nicht arbeiten), before a participle (nicht gearbeitet), before an adjective (nicht gut), before a place (nicht zu Hause). Otherwise, at the very end.