Hi Muhammad, I'm going to answer to the first question.

To start I suggest to read some books, where you can easily find anything you need from an expert, technical point of view. I really love books from O'reilly http://oreilly.com/css-html/index.html and from Manning http://www.manning.com/crowther2/ , but even those from Sitepoint are quite interesting http://products.sitepoint.com/ .

Then, while reading, build some website and try, try, try till the end of the days, because experience is very important in building correct html - css websites.

I don't think it's very important to learn php at the beginning, after your html books you could buy some about php.

Well I think it's correct what both SirMax and Jose Garcia Jr say, web 2.0 was an incredible change in the that way eaverybody could use the web and interact in it. Actually everybody can open a new blog for free, can write on the other blogs, can interact with friends in the social network thanks to web 2.0 social view. Before this, websites were only static paper-like advertising posters with no interaction possibilities.

I can't say if this change drove to a new graphic style or if a new graphic style helped us to change, now the web 2.0 style, made by gradients, glossy buttons, and icons as J.G Jr said is a standard.

Obviously web 2.0 style doesn't mean automatically web 2.0 intercatcion, it could be good for some tasks, less for others, it depends on what your website's made for.