The simplest way is to upload your favicon through the theme settings. Go to Appearance, click Settings next to your active theme, and look for a Favicon section.
Upload an ICO or PNG file and save. Drupal will serve the favicon automatically. For more control, place a favicon.ico file in your theme’s root directory and Drupal will use it by default without any settings changes.
For modern sites, you may want to serve multiple favicon formats for different devices. Add link tags to your html.html.twig template or use a module like Favicon. Good practice is to include a standard favicon.ico, an SVG favicon, and apple touch icons for iOS devices. This ensures the site looks polished across browsers and when bookmarked on mobile devices.