"It is not in the oven."
Translation:Nem a sütőben van.
If you move the words around that "nem" and "van" end up next to one another, then they morph into "nincs". But if you want to negate something else, like, in this sentence, the oven, then you have "nem a sütőben", so there is no place for "nincs".
However, it isn't necessarily a negation here. Like, if you take this example: - Your cookie is in the oven. - It is not in the oven. I've just checked it. then it can be "nincs a sütőben" as well. Depends on the context