Manual

Most UNIX systems have online manual pages.

MAN(1)                     OpenBSD Reference Manual                     MAN(1)
NAME
    man - display the on-line manual pages
SYNOPSIS
    man [-achw] [-C file] [-M path] [-m path] [-S subsection] [-s section]
        [section] name [...]
    man -f command
    man -k keyword
DESCRIPTION

The types of manpages have sections which they are grouped in. Here is the manual page layout of BSD:

Section 1

General commands (tools and utilities)

Section 2

System calls and error numbers

Section 3

Library functions, especially for C and Tk

Section 4

Special files and hardware support

Section 5

File formats, especially configuration files

Section 6

Games

Section 7

Miscellaneous information pages

Section 8

System maintenance and operation commands

Section 9

Kernel internals

When someone tells you to run "man 6 tetris", that means that you should read the tetris manpage found in section 6 of the manpages. Sometimes the same manpage name exists, but in different sections. One example is the fstat manpage it exists in sections 1 and 2. The lower number sections take precedence over higher numbered sections. Thus, to see the manpage for fstat in section 2 you would type:

$ man 2 fstat

Similarely functions, syscalls or commands are sometimes mentioned with the section of manpages in brackets behind them like so: fstat(2), you'll see this mentioned a lot in this wiki.

It is possible to do a keyword search in the manpage system.

$ man -k filesystem
OpenBSD::Vstat (3p) - virtual filesystem for pkg_add(1) simulations
dump (8) - filesystem backup
fstab (5) - static information about the filesystems
...

Another command synonymous to man -k is apropos:

$ apropos archiver
tar (1) - tape archiver

Do notice that the section of the manpage are displayed in the keyword search, this is to ease viewing the particular manpage.