WordPress API for Templates

API function list for Template Tags in WordPress is here

WordPress API for functions

WordPress Template Tags The API for WordPress functions is here. Post, Page, Attachment and Bookmarks Functions Category, Tag and Taxonomy Functions User and Author Functions Feed Functions Comment, Ping, and Trackback Functions Action, Filter, and Plugin Functions Theme-Related Functions Formatting Functions Miscellaneous Functions Classes WordPress Variable Report WordPress Hooks Table

WordPress Codex – Designing headers

Everything you wanted to know about designing Header Images in WordPress but were afraid to ask. Even changing header images

WordPress Codex

The definitive guide to doing anything with WordPress, from the horse’s mouth: http://codex.wordpress.org/Advanced_Topics They have the WordPress Codex function list among other valuable things.