All what you need to know about PHP from A to Z: 
The PHP is a scripting language, you need to build the related web pages with the extension .php;  it is a programming language that can do all sorts of things like: build login forms, communicate with servers and databases, evaluate data sent from a browser, build custom web content to serve the browser, and even send and receive cookies. The php coding help, in particularly, to build dynamic and interactive Web pages. 

The fourth basic things to know about the php Lang:
  • The PHP runs at the server while the JV runs only in the browser, or at the client side.
  • The PHP code is written like this: <?php echo "I'm learning PHP!";   ?>
  • The file should be saved with extension  .php
  • The comments should be putted after //


All what you need to now about the  HTML 5
The HTML 5 new elements are : header, footer, section, article, nav, aside, figure, figcaption, time, main;so there is one rule all content putted outside these elements will be considered as default content. 
For better SEO indexing you will have to apply Microdata.