Hiya! Yeah, I was saying not to rush things - sit back and practice with baby steps to figure out how things work, and it'll give you ideas as to how to achieve the texture you have in mind.

Digital camera in repair? I'd just sit in the corner and cry if that were me! Can't live without my camera(s)!

Okay, PART of a layer to be transparent: 1 of 2 quick ways
1 - Eraser tool - you can set the opacity of the Eraser so that it doesn't COMPLETELY erase things (you can also make it a hard edged brush or soft edged) - just somewhat at a time. Not my favorite way as once it's gone, it's GONE.
2 - My favorite way (and the illustration I attached) - click on the layer you want part of to be transparent. At the bottom of the layer palette click the Layer Mask Icon - little white box will appear. Get your Brush Tool (you'll notice your colors go to black and white) and lower the opacity - try 30% for starters. Hit F5 and click on "Brush Tip Shape - which is in BLUE in the illustration - then choose your hardness. Whatever you paint BLACK will hide what's on that layer - if you paint too much, paint WHITE to see it again.

Why do I like #2 better? It's editable - if you go to far, you can bring it back - it's still there, and you're just hiding the parts you don't wanna see.

The bit about "bumps advice" is just that if you are looking to make it REALLY rusty, you'll be making more extreme bumps of the material - if it's too shallow/flat it'll just be a color texture. I was just giving you a guide to follow if you wanted it shallow or deep.

I think part of the challenge of this thread is that "what you want" is completely subjective to you. We can come up with tutorials to do this or that, but it's probably not be what YOU are looking for, and will just add to your frustration.
I'm a fan of partial rust for my stuff, and colored liquid damage, but above it looks like you want serious rust for the whole thing, so we're not too sure what to suggest as far as achieving a specific image/texture.

BTW - your image from the tutorial looks good! Keep going - they just suggested a decal or something - you can just leave it at that or add more stuff of your own.

Hope this helps-
-Lew ;-)