So what do you want to know? HTML5 is the latest version of HTML, and includes easy ways to include audio and video in your web pages, among many other things. CSS3 is the third version of Cascading Style Sheets, which tell the browser how to lay out your web pages. (The philosophy now is to separate the layout of the page from the description of the content, so we no longer use tables to arrange things on the page, just to present tabular data.)
One offshoot of this is that web browsers can report the capabilities of the device they’re running on–things like screen size, device orientation, device location, etc. this means that web pages can automatically adjust themselves to the size and shape of the screen they’re on. This is called ‘responsive design’ and it’s big these days.
PHP is a language that runs in the web server and automatically builds web pages to predefined specs by basically filling in variables and outputting the results in the finished web page–and it can choose what to fill in based on user input from a previous page, or do so as a result of looking things up in a database.
So, where do you want to go?