At its most basic, index. php is the first file that will show up when a browser goes to the site or a directory. Beyond that, it can be used for whatever the site/project dictates. For more complicated sites or frameworks, it acts as the "boot" script.

Navigate to "localhost:8888" in your browser's address bar. The address bar is where you normally see "https://www." To do this, type "localhost:8888" and press ↵ Enter (Windows) or ⏎ Return (Mac). You'll see a directory of your PHP files displayed on the page. Click the PHP file to run the script in your browser.

Go to the location of your PHP file, then click the PHP file to select it. Click Open. It's in the bottom-right corner of the window. This will open the PHP file in Notepad++, allowing you to view the file's code and make any necessary edits.

Web developers and others who are knowledgeable about web pages know you can use a browser to view the HTML source code of a website. However, if the website contains PHP code, that code is not visible, because all the PHP code is executed on the server before the website is sent to a browser.