Ok I feel like such a noob but I don't really know how to use a layer mask or what it really does. I never had needed it, but there must be a good use for it... Can anyone help?

Check out this tutorial done by Ledirlo
http://photoshopcontest.com/tutorials/9/masks.html

Later Masks are your friends.

Thanks but honestly I must be retarded because I dont't see why you would need to do that... Are there any other ways to use masks? And please explain like I am 5.

Yes, use your imagination" Gradients, blurs, feathering, channels, ect.....

If you want to cut out a piece of the picture, use a layer mask.

If you want to hide a piece of the pretty picture, use a layer mask.

Homework:

http://www.photoshopcafe.com/tutorials/blend/blend.html

http://veredgf.fredfarm.com/tuts/mask/masking.html

http://www.lunacore.com/photoshop/tutorials/tut003.htm

I personaly ALLWAYS use masks and NEVER use eraser tool... the thing about masks is that you can hide, rather than erase part of the picture and therefore you can unmask a part of a layer or group if you feel that something went wrong.
One more thing is that you can do various blends with masks, just like in the tutorials DP posted without actually using the eraser tool which isnt too handy for it, especially if you want a smooth transition, and you can even paint on a mask, blur it, apply various filters and all that kind of stuff and it will affect the layer (or group) it is linked to...
Once you become a little more familiar with them you will start to see their true power

layer masks are sexy

but Dot's sexier

Layer Mask vs. Eraser

Layer mask works with black & white brush. You paint black on the layer mask the parts that you want to hide and white on the parts that you want to make visible.

Works exactly the same except the eraser actually gets rid of the parts of the image you erase. If you open your PSD back up, it's gone. You can't get it back.
With a layer mask, you simply mask out (with black) the part you don't want and when you open up your PSD next time and find that you need a little more of the layer to be visible, no problem it's all still there.

Now, if you are done and are sharing your PSD with someone else or want to shrink the size of your PSD, then apply the layer mask and it will just erase all the parts that are masked out and your PSD instantly shrinks in size (like magic!).

Layer Mask!
Layer Mask!

Sometimes you
Are Hard To Know...

And yet,
In the Knowing
You give
So Much.

A million thanks is not one drop in the ocean
For what You have Given Me.



(Yay Layer Mask!)*
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*See excellent posts above for reasons

I have never use layer mask... I can't find a real use to them.

Ditto that. I've never used them, I find masks annoying. I just find other ways to do the job.

RE: ssshisto's request...this IS "Ask the Experts" afterall. He's asking a logical question.

DP, some great examples. Was looking for that Lunacore tut myself for him.

Where the hell is Ledirloo??? Where the hell are the Experts?

C'mon ppl...step up!

ah, and Rein, just keep playin the accordian and singin'. We'll learn to live w/ it.

refusing to use layer masks is like stating that the earth is flat. An absolutely key element of photoforgery.

eraser, you are history