Open up your favorite text editor. The simpler the better; TextEdit or WordPad are better than using Microsoft Word. Begin your document with <?php and end it with ?>. Now go to File >> Save As…, type in a name, and save it to your desktop. Now close the text editor, navigate to that file on your desktop, and make sure it ends with “.php” instead of “.txt” — you can simply rename it and that should take care of things.
Google might help you find answers to questions like this much faster:
https://tinyurl.com/makephp
This one is pretty much what I just typed:
https://answers.yahoo.com/question/index?qid=20080322015613AAfTZ80
