iPhones, iPads and iPod Touches can all display a special homescreen icon for your site when a user saves the site to their homescreen. it's a lot like having your own iPhone app.
To participate, all you have to do is create a square image in the .png format, 129 pixels wide by 129 pixels tall (this is the size Apple uses for their own icon). Do not try to add the "shadow" to the icon yourself. Your Apple device does this automatically.
Now name that file apple-touch-icon.png (important: this must be the exact name, and it must genuinely be in PNG format, not just a renamed JPEG or GIF file; only PNG will do).
Next, click the left-hand menu on your website and pick "Customize Appearance."
Third, click the "Advanced Editor" heading. The advanced CSS editor will appear.
Now look over on the right for the "Upload Asset Images" button. Just click this button or drag your apple-touch-icon.png file to this area.
Now you're ready to try it out! Just visit your site with your iPhone and add it to your homescreen as you would any webpage.