Manual

Most UNIX systems have online manual pages. The types of manpages have sections which they are grouped in. Here is the 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.