How to save it as an icon on the home screen of the smartphone

Android
When your digital business card is open into your browser click on the menu at the top right (see image). In some models it is at the bottom.
From the various options choose "Add to Home Screen".
Click Add.
All done. Now share your digital business card with whoever you want.

iOS
When your digital business card is open into your safari browser and click on the share icon at the bottom of the screen (see image)
From the various options choose "Add to Home Screen". If you don't see it, scroll through the various options.
Click Add.
All done. Now share your digital business card with whoever you want.