sir
The German word 'Herr' is used as a title of respect or form of address for a man. It is equivalent to 'Mr.' or 'Sir' in English. 'Herr' is also used in German to refer to a man in a general sense, such as 'der Herr' meaning 'the man' or 'the gentleman'. In German, 'Herr' is capitalized when used as a title, but not when used as a noun.
Good morning, Mr. Schmidt.
This is a common formal greeting used in the morning. 'Herr' is the equivalent of 'Mr.' in English and 'Schmidt' is a common German last name.
Mr. Weber, the coffee is ready.
In this sentence, 'Herr Weber' is being addressed directly to inform him that his coffee is ready. 'Weber' is another common German last name.
I will tell it to Mr. Müller.
In this sentence, 'Herr Müller' is the indirect object, the person to whom the speaker is going to tell something. 'Müller' is a common German surname.