The process:
- Create a 60x60 pixel, 72dpi PNG image for your icon file (57x57 is the actual icon size, but we're hearing 60x60 works best)
- Name it "apple-touch-icon.png"
- Throw it in the root folder of your website. (Not the root of your server, the root of your web documents.)
If you need, for some reason, to specify a different location from webroot or a different filename, you can do so by specifying the image location with an entry in your page's HEAD section:
<link rel="apple-touch-icon" href="/whatever.jpg"/>
The iPhone / iPod touch takes care of the rounding of the edges and the rounded, gloss compositing that makes it appear to be a button with depth.