If you’re going to code (HTML, CSS, PHP, or any language) you’re going to need a text editor.
I’d recommend Sublime Text. It’s free, AND it’s the best. Here’s a super quick video on how to download and install Sublime.
Note: Sublime is free, but until you purchase it you will get a pop-up asking you to pay. Feel free to press escape (to ignore), or to buy a license.