"What do you need?"
您 is the formal form of 你. In English, "you" is used for all people in all situations, but in some (or many) languages, there are informal & formal (politer) you. - 你 (informal you): We use it to talk to people younger than you, peers, (best) friends, etc. - 您 (formal/politer you): We use it to talk to people older than you, people that we respect or we recently recognize, e.g. parents, teachers, bosses, presidents, etc.
您 is a formal form of 你, sort of like usted in spanish or vous in french. A shop owner might refer to a customer by 您. Im not sure about all of the appropriaye uses, but it's more formal or polite.
If you're going to say 你 is wrong you should indicate in the question that we need to put the formal version.