First, you'll need to download the Wallpaper Engine app, which is available on Steam. Once you've got it installed, you can browse through the massive library of user-created wallpapers. You can search for specific themes, like anime or gaming, or just browse through the popular section to see what's trending.
When you find a wallpaper you like, just click the download button, and it'll be added to your collection. You can then set it as your desktop background, and even customize it with animations and effects. It's so cool to see your desktop come to life!