How could you convert a color image to grayscale?

Magic Eraser tool...

How to be able to open RAW files in Photoshop?

How do you hide or show all panels, including the Toolbar and Control Panel.

Which color mode can be converted to Duotone?

You've adjusted the size, hardness, spacing, etc. to a brush; how do you add it to your Brush Palette?

What do the width and height of the histogram in levels adjustments represents?

How 'Expansion Field' of Puppet Warp tool work?

Substractive color system used for?

Using Render filters, you can

Option to change the Background layer's appearance when part of your image is transparent?