A favicon is a graphic image (icon) associated with a particular Website. The format for the image must be 16×16 pixels, 32×32 pixels, using either 8-bit or 24-bit colors.
To change or add Favicons you need to head into Global Settings ➡ Head / Footer areas.
There’s 2 types of Favicons:
The Standar Favicon for all browsers and devices.
Apple touch icon
Similar to the Favicon, the Apple touch icon or apple-touch-icon is a file used for a web page icon on the Apple iPhone, iPod Touch, and iPad. When someone bookmarks your web page or adds your web page to their home screen, this icon is used.