Every icon your website needs, from one image.
Start from your logo, or from a letter or emoji on a colored square. You get favicon.ico, the Apple and Android icons, a web manifest and the HTML to paste in.
Font
Style
Background
Add them to your site
Put the files from the ZIP in your site's root folder, then paste this into the <head> of your pages:
<link rel="icon" href="/favicon.ico" sizes="32x32">
<link rel="apple-touch-icon" href="/apple-touch-icon.png">
<link rel="manifest" href="/site.webmanifest">