Here's the best way to fix a scratch on your car
First off, if you don't have time to repair the scratch right away, you should ...
Cover it with a piece of tape
Duct tape is good for this. You should keep a roll in your car anyway, for emergency repairs. The old-school silver-gray tape advertises that something is amiss, but you can now buy duct tape in so many different colors that you should be able to find some to match your car's tone.
This is a temporary solution, however, a way to prevent water from getting into the scratch and promoting rust.
You have two better options, as long as the scratches are wide or so deep that they could be called gouges:
1. A scratch-repair kit
A scratch in your car's finish is fixable without a lot of effort if it isn't deep or wide. Superficial scratches are in what's called the "clear coat," a layer of finish that's transparent and protects the color underneath. A scratch-repair kit, like this one, enables you to blend the scratch into the rest of the finish without having to match paint. It won't look like new, but it will fix the scratch.
2. Touch-up paint
This is more involved. First, you need to go to an auto-supply store and have them match the touch-up color to your make and model of car. Next, you need to clean and lightly sand, using fine-grit sandpaper, the scratched area. Then you need to apply several coats of touch-up paint, allowing it try dry in between. After some more light sanding, you apply new clear coat (which can also be purchased at an auto-supply store). When it dries, you wax the area.
This will give you a good scratch repair that restores the structure, if not the appearance, of your car's factory finish.
Small dings and scratches are a way of life of you own a car. It's a good idea to deal with them right away. Later, if you plan to keep you car and want it have a relatively pristine appearance, you can wait for the damage to add up and head to a body shop for a full suite of proper repairs. This will of course be far more expensive that the $20 to $50 you might spend on a repair kit or by going the touch-up route. I like to say that a trip to the body shop always equals $1,000.
Just don't prep your repair by coating the damaged area with gray primer and then forgetting about it! That signals your inability to get the job done.
You should repair scratches as quickly as possible. Once the sheet metal under the paint is exposed, it's only a matter of time before the rust has a chance to take hold.