Hi Lux. Require means to need (or to be compulsory). I require 3 students a day to make money teaching on italki. You are required to wear a seatbelt in a car. Demand is to ask for something in a forceful way. I demand you get off the phone right now. I demand an explanation for your lateness

"Demand" is confrontational; "require" is not.

require is seek or searching and also give order for something demand is peremptory else by using power comand some one.