This article explains how to personalize your Mac by changing folder and disk icons. The instructions apply to devices running macOS 10 or later.
There are many icon collections available on the web. The easiest way to find Mac icons is to search for the phrase "Mac icons" in your favorite search engine. You will find numerous sites that offer free and cheap icon collections for Mac, including IconFinder and Deviantart.
Once you've found the icons you want to use online to personalize your Mac, here's how to customize your desktop.
Find an icon set you want to use online and download it to your Mac.