Japanese HELP!?!!?!!!?

Question

Someone please explain the difference between nan and nani

they both mean "what" but I dont know when to use nan or nani in a sentence

Answer 1

if nani comes before "desu" in a sentence then it is usually said "nan". if not than you can just use "nani"

Answer 2

It depends the position of usage. No one says nani desu ka. In front of the d of desu, the i of nani is dropped.