Codepen provides the boilerplate for you. It only expects the code you’d put within the body element in the HTML editor. (No need to include the body tags). For anything you want to add to the <head> element click on the ‘Settings’ button, then HTML and add it into the ‘Stuff for <head>’ box.
Basically, you are not linking to font awesome correctly.
The JS editor in codepen is for JavaScript code.
Side note: the correct format is this <script src="https://kit.fontawesome.com/a076d05399.js" crossorigin="anonymous"></script>
Is this a076d05399.js yours? Asking because it’s not working however if I put in mine I do see the icons. If that is yours it appears to be corrupted so try and get another.
Also, you should get as many as you can of the user stories to pass prior to styling this way you’re not trying to make things fit by working back and forth.