Basically, a totalitarian government is one that tries to control every aspect of the lives of its people. It is usually a dictatorship, but the most important thing that sets it apart from other forms of the government is the fact that it tries to control its people so completely.
In recent times, the best known examples of totalitarian governments have been those of Nazi Germany and Soviet Russia. In those countries, the dictators tried to use intimidation and persuasion to control their people. They tried to make the people love and honor the dictators, for example. They tried to make them believe in the superiority of the Aryan race (Germany) or the inevitable triumph of communism (Soviet Union). They even tried to affect the way their people looked at marriage and family life.
I suppose that a good example from more recent times is the Taliban in Afghanistan in the late '90s and early 2000s. They tried to control people's lives down to their facial hair, their clothing, and what they did for entertainment.
That is what totalitarianism is -- when a goverment tries to control every aspect of its people's lives.