How do I make a background only visible through a certain part of a photo?

[WayMoreConfused]

I looked through the forum and couldn't find quite what I'm looking for. Say I have a blue background and I want that background to only be visible through a square on the photo and the rest of the image is unchanged. I think I'm wording this right. Also, is it possible to do with text? Thank you in advance.

[barbieq25]

Put you background on one layer & your image on another layer above it. I would copy the image layer in case something went wrong or I changed my mind, but hide it for the moment

Then on the image layer that is not hidden, cut out the square where you want it to be & you should see the blue underneath.

[Cc4FuzzyHuggles]

This is pretty much the same as what Barbieq said.
 
It sounds like you will want to work with several layers. So, try this :
1st Layer/Bottom Layer -- Make Blue
2nd Layer /Middle Layer -- Your Picture's layer
3rd Layer/Top Layer -- Duplicate your picture and have it be your top layer
 
Make your top layer invisible for now. (It's only there for referencing and in case of mistakes.)
Next, on the middle layer, make holes in it so that the blue layer shows through. To do this, you can either use a selection tool and delete areas, OR you can erase areas with tools. For erasing, you can use the eraser tool, or you can use other tools with their blending mode set to "Overwrite" and your primary color set to "Opacity - Alpha 0".
 
Sample Images :
Use Three Layers

 
Optional, erase using overwrite blending mode and Opacity - Alpha set to 0.

 
Here are different ways to make holes in an image. The Checkered squares represent transparency.

 

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For text, try exploring text effect tutorials, and see if any teach you techniques that do what you're looking for.

http://forums.getpaint.net/index.php?/forum/23-text-effects/

 

 

Have Fun, and good luck getting creative now.

Edited July 11, 2014 by Cc4FuzzyHuggles

[WayMoreConfused]

Thank you both for the very informative answers. I was a little lost for a bit. Very helpful stuff!