GIMP Version: 2.8.14
Operating System: Windows
OS Version: Win10
GIMP Experience: Intermediate Level

List any relevant plug-ins or scripts:
No plugins/scripts

List any ERROR messages you received:
No errors

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Hello there!

First time trying to use a layer mask. I've followed gimp's instructions and multiple youtube videos' instructions as well... but whenver I add a layer mask to my top layer, it hides the entire layer, which makes it literally impossible to do what I'm trying to do. Any help would be appreciated!

Thank you in advance.

Have you tried checking/unchecking Invert Mask when you create the mask?

I presume it hides the top layer.

How layer masks work:
Black hides (makes transparent)
White displays (makes opaque)

Best guess is that your layer mask is black. Select the layer mask in the layers dialogue and bucket fill it with white.

I appreciate the tips. We can call this one solved... I don't know WHAT I was doing wrong, but I tried it again and magically its working fine. It IS a very very large project, so I assume my computer was trying its best to keep up, but wasn't hitting the mark.

Thank you again!