I understand the initial confusion. Here's the way I explain it in my workshops. Think of the "high resolution" shot that you originally recorded with your camera as your "digital negative." This "master" enables you too make a photo-quality print, if you choose, at the maximum size your camera allows (5x7 for 2 megapixel, 8x10 for 3 megapixel, etc).
But, in this case, you want to use those same images for your website. So then you open your "master" in an image editor, such as Photoshop Elements, make a copy of it (Save As), then resample down that copy so it is a small, web-servable file.
Your original image is safe and sound so you can always return to it for other uses.
The thing to remember is to keep your master files at high resolution, then make copies of them.
I hope this helps...