What would you like to learn about them?

Basically they store mask information. This lets you manipulate and isolate specific areas of your image. It's very useful when working with multiple layers. Especially if you don't want to do "destructive" editing to a part of the image (destructive editing is any pixel manipulation that alters the original ie... erasing, smudgeing, blur...)

On the Adobe site there is a great resource area (Expert Center) you just have to sign-up (it's free)

let me know if i can help with anything...
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