Man Pages Sections:

Section 1: User programs and shell commands

Section 2: Kernel functions

Section 3: Library functions

Section 4: Special files found in /dev

Section 5: File format descriptions and conventions

Section 6: Games

Section 7: Miscellaneous conventions

Section 8: Utilities used by root

Section 9: Kernel routines

To search across man pages for a keyword type man -k keyword.

Info

• The
  information displayed by the info utility is called a node.
• To
  Search for information in info, press ctrl-s and then enter your search
  term.

Readme files
usually contain the following types of information:

• Version
  numbers
• Program
  descriptions
• Change
  logs
• Installation
  and configuration information
• Known
  issues
• Bug
  reporting information
• Copyright
  information

README files are usually located in either
/usr/share/doc/packages or /usr/share/doc.

TLDP(The Linux Documentation Project) http://www.tldp.org

Linux vendor websites usually include the following:

• Knowledgebases
• Documentation
• Support
  forums