Interesting post. Also looking some responses here. I guess it should be linked as per my knowledge html is in which designers are expert and php is in which developers are experts. So two Ds always worked together
HTML is a markup language used to display information on a web page. PHP does something similar except it is server site programming language. It interact with databases, evaluate conditions statement, system information and spit it out at the client and on the client side, this give displayed as HTML.
A simple way to explain it would be that HTML is the skeleton of a website, CSS is applied to the HTML for styling. PHP is more for functionality. For example if you were to create a static page to display information and doesn't have any functions such as a login, members area then you would be using only or mostly HTML and CSS. If you wanted to create a website that has additional features such as the above mentioned, or has dynamic features such as a page counter, then PHP is needed to execute these functions.
HTML is used to create static website while php is to make dynamic site. PHP code is embedded within the html code using <?php and ?> tags. PHP is server side script language while HTML is markup language.
PHP files are just like HTML files, but they can include both HTML and PHP code. The PHP code is parsed (or executed) by the Web server when the page is accessed and the resulting output is written as HTML within the Web page. When a user accesses a PHP page, his Web browser only gets sent the HTML code, since the Web server has processed the PHP code in the background. Most PHP pages are processed so quickly that it does not noticeably slow down the loading of the Web page.
The .php extension is important, since it tells the Web server that the page may include PHP code. Therefore, it must be run through the server's PHP engine before being sent to a client's Web browser. This allows dynamic content to be generated each time the Web page is loaded, based on the variables included in the PHP code. For example, PHP pages may load objects such as the current date and time, data from form fields submitted by a user, or information from a database. Still, once the page reaches the user's Web browser, everything is formatted as HTML.