The WordPress Codex is the name given to the primary WordPress documentation that lives at codex.wordpress.org. The Codex contains information for all level of users, from those who are just starting out and trying to understand what features WordPress offers, to advanced WordPress developers looking to for specific details on template tags and plugin hooks.
How to Use the WordPress Codex
The WordPress Codex is the name given to the primary WordPress.org documentation that lives at codex.wordpress.org. The Codex contains information for all level of users, from those who are just starting out and trying to understand what features WordPress offers, to advanced WordPress developers looking for specific details on template tags and plugin hooks.
Extra Credit
After taking a look over the Codex, see if you can find a way that you can help contribute to this living WordPress documentation.

TreeHouse The WordPress Codex