How is a national census conducted?

Census takers are hired by the U.S. Government, prior to the census taking. They are trained in how do do this, for a few weeks(I believe) , then go door to door, and ask questions from the papers they are given, and fill them out accordingly. The questions are usually, How many people live in this household? How many are adults? How many children? How many fulltime residents live here? How many part time residents live here? How many are enrolled in school?(College,grade school, ect). How many work fulltime? Who is the head of household? How many male or female? Is the address we have accurate? I believe they do ask what race are the residents(but I cannot say if you have to anser or not, same with religion)