Layers Question in PS 5.5

Hello,

Hope this is the right forum. Simple question:

I create a new file with a white background. Next I open a digital color image. I select and move a portion of the digital image onto the first, white layer. I transform the image. I select the image layer and apply a gradient to the image layer and it covers the entire canvas, which I do not want.

How do I apply filters only to the image layer? I want the original background to act as a frame.

Thanks.