I just loaded a 6 meg photo that came from a Casio P600, into Photoshop Elements.

Click: Image/Resize/Image Size

At the top I see 2816 x 2112 pixels (6 megapixels)
At the bottom I see 39.111 x 29.333 inches at resolution 72.
(this tells me that if I printed this photo at 72 dpi it would be huge).

Now

If Resample Image has a check mark - remove the check mark.

Now change the resolution to 300.
The image size changes to 9.387 x 7.04 inches.

(if I printed this photo at 300 dpi, the result would be 9.387 x 7.04 inches)

Change any figure in the bottom area and the other two figures will change. Notice that the figures in the top half never change.

...

Now if you check mark "Resample Image" and change any figure at the bottom, the figures in the top half of the window will change.

This is telling you that when you Click OK, the image will be resampled and the original image will be resized.

...
..
.