man (short for “manual”) is a traditional form of online documentation in Unix
and Linux operating systems. Specially formatted files, “man pages”,
are written for most commands and distributed with the software.
Running man somecommand will display the man page for (naturally) the command or program somecommand.
there are so many of them, man pages are grouped into enumerated
sections. This system has been around so long that you will often see
commands, programs, and even programming library functions referred to
with their man section number. For instance, you might see man(1). This tells you that man is documented in section 1 (user commands); you can specify that you want the section 1 man page for “man” with the command
#man 1 man
#man – S 1 man