Learn French: Je ne cuisine jamais de champignons.

In French, jamais replaces pas to mean never. The structure is just like ne ... pas, where you put ne before the verb and the negative word (jamais) after it. You do not use pas and jamais together in the same sentence.

Why is it de champignons and not des champignons since mushrooms is plural?

This is a very important rule! In a negative sentence, plural articles like des change to de. So, I cook mushrooms is Je cuisine des champignons, but as soon as the sentence becomes negative, it changes to Je ne cuisine jamais de champignons.

I know cuisine means kitchen. Is it also a verb here?

Yes! Cuisiner is the regular verb for to cook. Because the subject is Je (I), we drop the -er ending and add -e, giving us Je cuisine. It is spelled exactly like the noun for kitchen, la cuisine.

Do I pronounce the final s at the end of jamais and champignons?

No, the final s is silent in both of these words. In French, you usually do not pronounce the consonant at the very end of a word unless it needs to link to a vowel in the next word.