There is a huge wealth of help and reference material available from the command line. Almost every command has its own man page, which is a (usually) complete manual for all of the options and the usage of the command.

The system manual is divided up into sections:

Throughout this and most documents, commands are specified together with their man section. For example, man(1). To read a man page, just type:

chaos[1] % man [section] name

And you will see the proper page come up:

MAN(1)                  FreeBSD General Commands Manual                 MAN(1)

NAME
     man - format and display the on-line manual pages

SYNOPSIS
     man [-adfhkotw] [-m machine] [-p string] [-M path] [-P pager] [-S list]
         [section] name ...

DESCRIPTION
     Man formats and displays the on-line manual pages.  This version knows
     about the MANPATH and PAGER environment variables, so you can have your
     own set(s) of personal man pages and choose whatever program you like to
     display the formatted pages.  If section is specified, man only looks in
     that section of the manual.  You may also specify the order to search the
     sections for entries and which preprocessors to run on the source files
     via command line options or environment variables.  If enabled by the
     system administrator, formatted man pages will also be compressed with
     the `/usr/bin/gzip -c' command to save space.

     The options are as follows:

     -M path     Specify an alternate manpath.  By default, man uses
                 manpath(1) (which is built into the man binary) to determine
                 the path to search.  This option overrides the MANPATH envi-
                 ronment variable.

If you do not know the section, you may omit it.