In German, a man (an adult male human) is Mann. When you're talking about a hypothetical generic person, you use "man," which sort of correlates to the English generic pronoun "one." (As in, "One does not simply walk into Mordor.") Then there's also the word "Mensch," which in German can be used to mean a human being of either gender even though the noun itself is grammatically masculine. Or, alternatively, you can use Mensch as an exclamation of dismay, like, "Oh man (Mensch), the weather is so hot today!"