In two words what I understand how far is made of the audience measurement?

Who decides? They are groups of media professionals, agencies and advertisers who decide the choice of methods and means to implement and determine, by calls for tenders, which will be the operating institutes. How is it done? For radio, it is usually surveys by telephone or self-administered questionnaires on paper or via the Internet or continuous waves. For television, these are books of hearing or people meters to push buttons. Some systems, yet rare, using people meters individual phones. Who pays? These devices are primarily funded by the media who want their audience to be measured.