What is XML ,CSS ,XHTML???? how they differ from HTML???

XHTML is a advanced version of HTML. CSS is stylesheet support. XML is for data calling. Visit w3schools.com

HTML is the Basic thing for Web Pages. It is for displaying the content onto the web. CSS for formatting the content which you want to put onto the web page. xHTML is based on HTML, but has some differences. XML is mainly used for Data Storage. Check: http://www.sitepoint.com/forums/showthread.php?t=393445 It has the FAQ for HTML and xHTML.

CSS are lines of code to enhance the design of your webpage. for example you can the color of your text through CSS, you can make the text blink, add a background to your text. Choose whether to underline links or not, well, you can do a lot of things with CSS. You can even add hover effects to your pics, if you know the CSS codes. HTML is the code you use to build your page.