There are a number good programming guides available on the internet which can assist you with HTML, CGI and other commonly used programming languages.
This is an excellent HTML and XTML reference guide.
PHP is a scripting language that is embedded into HTML much like Mirosoft's ASP (Active Server Pages). Unlike ASP, however, this language can execute on various types of servers, not only Microsoft NT servers. This manual explains how to write dynamic web pages using this server-side scripting language.
This provides further information for PHP developers.