As already replied above, html is a markup language to create a static web page directly.
php is a server scripting language used to create html pages at the server, interact with a database of (for example) HELP posts like this.
This web site is comprised of php scripts to create the millions of pages that make it.
There is not a horde of programmers retyping every altered page whenever somebody adds a post :P
Start with html, css, php, mysql,
with each there are good tutorial sites, heaps of code samples, prewritten scripts under gnu to base your own work on.