"I do not want bread."
Translation:Я не хочу хлеб.
Word order is flexible to a point. By putting не before хлеб you're changing the sentence from I don't want bread to kinda of like I want something but not bread. Also negating bread will I believe require the хлеба genative case, whereas in the accepted answer either accusative OR genative can be used.
These are simply conjugations of the verb хотеть.