http://codex.wordpress.org/Function_Reference
how to use query
http://codex.wordpress.org/Template_Tags/query_posts
this one explains how wp gets and displays posts
http://codex.wordpress.org/The_Loop
and template Hierarchy
http://codex.wordpress.org/Template_Hierarchy#The_Template_Hierarchy_In_Detail
http://codex.wordpress.org/Conditional_Tags
http://phpxref.ftwr.co.uk/wordpress/nav.html?_functions/index.html