Web Interface for Raspberry Pi

I'm trying to control a led on  raspberry pi 3  using apache server  with  php programming. I am following this instructable link 

https://www.instructables.com/id/Simple-and-intuitive-web-interface-for-your-Raspbe/  

I have tested server, its working with simple php program but when I write program for led, it doesn't work When I check file it say permission denied 

How to resolve this issues ?