du and Sie

     As native English speakers, we all understand the differences between calling our elders by their title or calling them by their first name. There is an unspoken boundary between using family names (also known as last names) and using personal names (also known as first names), and this boundary is present, even if we do not acknowledge it outside of addressing the other individual.
     In Germany, the distinction goes beyond merely addressing the other person, but also when speaking to them. This is carried on using the two 'versions' of the English word "you" which are "du" and "Sie". The informal version, "du", is how one would address their friends, family, and other individuals close to them. The formal version, "Sie", would be used in situations where you are first meeting, in a workplace, or in situations where someone has not announced that they are comfortable with you using "du".
     In America, a popular example would be television. In my favorite television show, Criminal Minds, this can be seen with the character Dr. Spencer Reid. He engages in many conversations with others, including co-workers, friends, and family members. When addressing his boss, he calls him "Gideon" which is his last name, and his boss will address him as "Spencer" or even "Doctor Reid". In Germany, this would basically be how the elder member (the boss) would address the younger member with "du" or "Sie" because he can, and how the younger would address the older with "Sie" because he should. Dr. Spencer Reid also speaks with Supervisory Special Agent Jennifer Jareau. They are friends, and therefore address each other as "Spence" and "JJ". This would compare with how Germans would address their friends with "du" and not with "Sie".

Sources:

Criminal Minds; Television Show created by Jeff Davis
Language Realm