The indefinite pronoun man is the 34th most common word in German. Despite appearances, it never means “man”. (That would be der Mann, which is number 131 on the top words list.) As a pronoun, man is a word that can be used as a substitute for a noun in a sentence. As an indefinite pronoun, man is a word that is not specific about the noun it stands for. It refers to one or more people with an unspecified identity.
Grammar of man
The pronoun man is never capitalized, except at the beginning of a sentence. It is used only in the nominative singular. It is a third-person singular pronoun (like er, sie, es), so verbs are conjugated accordingly.
In the accusative or dative singular, the masculine forms of the indefinite pronoun ein are used. It has no corresponding plural forms.
So, for example:
nominative: Was kann man tun?
accusative: Die Nachricht freut einen.
dative: Manchmal geht es einem schlecht.
The possessive adjective sein is used in lieu of a genitive form.
Man kann seinen Augen nicht trauen.
The nominative usage is far more common than the other case forms. The personal pronoun er is never used as a synonym for man.
Man weiß manchmal nicht, was man (not er) sagen soll.
Meaning and usage of man
(1) one, someone, a person, you, they, people
The German indefinite pronoun man corresponds in meaning to the English indefinite pronoun one (as in “One doesn’t do such things”), but is used more frequently and without the pretentiousness that one implies. Man is used where in English you is often used to mean people in general. Or man can be translated as people or an unspecified they.
Wie sagt man das auf Deutsch? How do you say that in German?
Man tut, was man kann. You do what you can.
Mit Reisen erweitert man seinen Horizont. A person expands his horizons through travel.
Man sagt, die Zeit heilt alle Wunden. They say that time heals all wounds.
Heute denkt man anders darüber. People think differently about that today.
(2) the passive voice in English
Man is frequently used in German where English typically uses the passive voice.
Man sagt, dass … It is said that …
Man hört, dass … It is understood that …
So etwas tut man nicht. That just isn’t done.
Im Deutschen nennt man sie Goldkäfer. In German they are called gold bugs.