Learn Dutch: Ik rook niet. - I do not smoke.

Dutch does not use a helper verb like 'do' to make negative sentences. While in English you say 'I do not smoke', in Dutch you simply say 'I smoke not', which is Ik rook niet.

Why does niet come after the verb?

When you are negating the entire action of the sentence, the word niet is placed after the verb. In short, simple sentences like this one, it goes at the very end.

The dictionary says the verb 'to smoke' is roken. Why does rook have two 'o's?

This is a spelling rule to keep the vowel sounding long. In ro-ken, the 'o' is long because it ends a syllable. When we chop off the -en to make the 'I' form, the 'o' is trapped between consonants. We have to double it to rook so it keeps that long sound.