What's the difference between "man" and "Mann"?
man (indefinite pronoun): "One," "you (generic)," "people." Always lowercase, only has nominative (man), accusative (einen), and dative (einem) forms.
Mann (noun): "Man." Always capitalized, declines like a masculine noun (der Mann, den Mann, dem Mann, des Mannes).
Example
Man spricht Deutsch hier. (One speaks German here / German is spoken here.)
Der Mann liest ein Buch. (The man reads a book.)