If there is still color left in the scratch, you are in somewhat better shape. This would indicate that you have only scratched the clearcoat. If you are through your clearcoat, you may not want to undertake the fix.
Assuming that you are going to proceed, I would purchase a clearcoat polishing compound. Apply compund to a soft cloth and buff the scratch using circular motions.
If the scratch is through the paint, you will need to clean the area with a good grease and wax remover. This preparation is critical to achieve good paint adhesion.
Purchase a bottle of touch-up paint at a local auto supply store. There should be a tag on your car that identifies the color number. Most auto supply stores will be happy to help you fine the correct color if you just ask for help.
Paint the damaged area with light coats of paint. you should allow each light coat to dry in between applications. You should allow at least 24 hours for the final coat to dry. To get that shine back, use a piece of wet-dry 2,000 grit sandpaper. Get the paper wet, and smooth out any imperfections in the paint. As a final step, you should wax the new paint. With a little practice, you should be able to make these patches look great.