Well one of my differences are the power of the people. In Democracy they can vote for the president. Also, they have a freedom of speech and the government do not control the people's lives at all. But in the other hand, the Authoritarian government they control the people's live and they have lack and limited power. They can’t vote for the president a group of individual.
How they are similar is that they have a government that can ask to pass laws. Our government is Monarchy which is a type