To see a sample of what the gallery looks like, go here or visit my GitHub for further information. Scroll down to the bottom of this page for installation instructions.
HTML: Okay, so! You want to copy and paste the HTML contents into a new file and save it as "index.html" (you can change index to whatever you want, I just suggest index since that's typically the default landing page webservers look for).
Next: CSS! Make another new file but this time copy and paste the CSS contents into it and save it as "style.css". Keep this file in the same folder as index.html and do not change this filename to something else unless you know what you're doing.
Lastly, JS. Make your final new file and copy and paste the JS contents into it. Save it as "script.js" in the same folder as index.html and style.css are in. Do not change this filename to something else unless you know what you're doing.
Voila! And there you have it! To preview your page, open "index.html" (or whatever you named it) in your web browser and you're good to go. Need further help? Email me.