To use PHP on your pages, it's best for them to have a .php extension rather than .html. (There are ways around this, but since you are starting fresh, changing the extension to .php is better.)
You need to give us more information on what you are trying to do. Do you have any PHP experience?
Also, are you building your site on your coputer, or it is already online? If it's on your computer at this stage, PHP won't work unless you set up a 'virtual environment'.