Go to the Eye icon on your Background Copy and click it, which momentarily removes that scan, but does not delete it. Then, click back on Background, and go up to the command items at the top of the Photoshop window, clicking on "Select" and then pull down to "Color Range." A window will open with a mini version of your artwork. Using the eyedropper, click on a white area of the artwork and press Okay. Your scanned image will then have what Mark calls "marching ants" running around the black areas of the image. Then, select your Eraser tool and click on a white area on this piece. The area you clicked should show a checked background (white and gray). If it does, then press your computer's Delete button, and all the white will disappear, replaced by that checkered background. This creates a transparency which will retain the line art while you color below it. At this point, I save the artwork, which it will do as a PSD document (aka Photoshop), retaining the layers.
Now, back on the Layers window, click the eye on the Background copy, turning it back on, restoring the white that was erased. Now, make sure that you have the Background copy selected on the right side of the box. As a test, select the brush tool on your toolbar and make a big streak across the page. If you have selected correctly, your swipe of color should show up while the lines in front remain fully intact. Because you're not going to keep it that way, you can do a Ctrl-Z to remove your test... or just color over it as you do the real coloring work.
For coloring it, you will just have to experiment with the tools. See what you can do. I use the Lassoo, Magic Wand, Brush, Gradient and Eyedropper quite a bit when coloring.