man is the system’s manual pager. Each page argument given to man is normally the name of a program, utility or function. The manual page associated with each of these arguments is then found and displayed. A section, if provided, will direct man to look only in that section of the manual. The default action is to search in all of the available sections, following a pre-defined order and to show only the first page found, even if page exists in several sections.
The UNIX Programmer’s Manual was first published on November 3, 1971. The first actual man pages were written by Dennis Ritchie and Ken Thompson at the insistence of Doug McIlroy in 1971. The troff macros used for man pages (-mm) were the general-purpose ones written by Ted Dolotta (later to be the first manager of USG and the principal author of the System III manual), with additions for the manuals. At the time, the availability of online documentation through the manual page system was regarded as a great advance. To this day, virtually every Unix command line application comes with its man page, and many Unix users perceive a lack of man pages as a sign of low quality; indeed, some projects, such as Debian, go out of their way to write man pages for programs lacking one.
All the man pages and hosted in this website for your reference.