>>6 Hypertext Markup Language (HTML) is the main markup language used for creating web pages. This is the first language you should learn.
Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation semantics (the look and formatting) of a document written in a markup language, such as HTML. Learn this the same time you learn HTML.
Hypertext Preprocessor (PHP) is a general-purpose server-side scripting language originally designed for Web development to produce dynamic Web pages. The code is interpreted by a Web server with a PHP processor module which generates the resulting Web page. Note that it is possible to convert PHP code to C++ code, improving performance as much as 50%, but that's too advanced for the learning stage.
Those are the basics. Learn them well, and then go on to C#, Javascript, Erlang, and XML.
There are also applications that you should check out, such as Adobe Dream Weaver.