I am new:) I am stumped as to how to crop out an image existing on a layer without deleting/hiding the rest of the content of all of the other layers underneath/around it. If I have an image that I want to crop down to 300x400 px, how do I retain the visibility of the other layers in the project that don't fall within that region? Do I have to open up the to-be-cropped image in another canvas, crop from there, and then reintroduce the cropped version to the original canvas? If so, how do I get a layer to temporarily be editable on its own canvas? Thanks!!
Use the rectangular marquee tool to select the area you want to crop and hit the "Add Layer Mask" button at the bottom of the layers palette. This will "crop" down your layer and leave the others untouched.