German has two main words for "not": nicht and kein. The split is simpler than it looks — kein negates a noun that has ein or no article (Ich habe kein Auto), while nicht negates pretty much everything else: verbs, adjectives, adverbs, and nouns with a definite article (Ich kenne ihn nicht, Das Buch ist nicht neu).
Word order also plays a role: nicht usually sits towards the end of the sentence but jumps in front of the specific element it's negating. The exercises below help you pick the right negator and the right slot in the sentence.
German Negation Exercises
In these next exercises, you need to decide whether to pick nicht or kein.
Nicht vs. Kein Exercise #1
Pick the negator that matches the noun (or non-noun) that's being negated. Three options here — nicht, kein, keine — so the article-style endings come into play too.
Nicht vs. Kein Exercise #2
Type yourself now, and choose whether it should be nicht or kein