A fast-paced, fairly light PBS documentary looking at the history of propaganda. 

Propaganda was once a word that was used by people to happily refer to themselves.  Edward Bernays, who helped convince Americans that getting into WWI was a good idea, wrote a book in 1929 he happliy called "Propaganda".  The word didn't yet have the connotations it would come to have after WWII and the Nazi party.  After all, convincing people of your ideas seemed a very normal thing for corporations and governments to do.  Once the term fell out of favour, terms like "Public Relations" and "Marketing" remained more acceptable synonyms.

Basically, people are trying to alter your thoughts, occupy a piece of your mind and identity, because someone paid them to do so. Somewhere in some boring, non-descript office, there are people with degrees in understanding the human mind, who get paid big bucks to get more people to eat junk food, more animals to go to slaughterhouses, or more people vote for parties that represent the economic interests of a tiny percentage of the population. You need to understand this in order to defend yourself from it and maintain some sort of personal and ethical independence.

This documentary will give you some pointers to get started understanding this system of social control.