|First off, you'll need a web server environment to run the PHP files. PHP is a server-side language, while HTML is a client-side language. That means you can just open up a HTML file in your web browser anytime, because the HTML code is interpreted by your web browser client-side. Read this guide on installing and using WampServer 2:|
Secondly, Notepad doesn't have the PHP file type as an extension, you save the file name as page1.php and the file type as "All Files".
Notepad is all you need for web development, but I suggest you instead use Notepad++. It's like Notepad on steroids with features like syntax highlighting, line numbering, and spell check. It also has PHP under the list of file types when you save.
Apologies if I don't respond to your reply immediately. I don't check this site daily, but you're welcome to PM me as a reminder.