"László is not an engineer, but a policeman."
Translation:László nem mérnök, hanem rendőr.
'Nincs' means "nem van" (I don't have a house = Nincs házam.) But never use "nem van", because it's incorrect.
Nem means "no" or "not". Nincs means something doesn't exist or there isn't any of it. Nincs and nincsen have the same meaning basically. Also, you can think of it as nincs = "nem van" (nem van is NOT said in Hungarian.)
Since you already know some Turkish: nem is a bit like hayır (no) or değil (not) while nincs is like yok (there is not).
Nincs házam = Evim yok "I have no house" (literally something like "my house does not exist" or "there is no house of mine").
My Hungarian teacher taught it as "nincs" = "nem van" also, because nem van is never said. Try to think of it as the negative third person singular form of the verb "to be". I walked into a store and asked for a pineapple and the lady said "nincs" ("there is none"- they didn't have pineapples at that store). "Nincs házam" doesn't have a literal English translation that's grammatically correct, but it would be something like "there is no house of mine".
i am wondering why not "...egy rendőr"? what am i misunderstanding i am wondering to myself...?