What each icon does what

As far as I know there hasn't been a "map" of the interface produced yet. However, take a look at the following resources. Individually, they don't each cover all the tools or menus, but maybe together they will weave a nice picture for you!

Photoshop Touch Interface Tour

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Link to Photoshop Touch Lays It On, which provides a nice overview of the software!

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Here is a Quick Start Guide to Photoshop Touch

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Additionally, there are many tutorials built-in to Photoshop Touch. Check them out, they will give you a solid overview of the app!

Cheers,

Michael