If your car has its original paint job, you can do an online search for your car's make, model, color, and the words "paint code." You can also look on the car for the code if you can't find it online. Check the door jam, near the VIN number, and on firewall (bulkhead) to find the paint code number. Go to your local auto parts store or contact your car dealership with your paint color in hand. If you have a common car, they will likely have touch up paint for your paint job in stock. If you have an unusual or rare car, they may have to order your touch up paint.  Touch up paint comes in several types of containers. It often comes in small jars of the paint or in paint pens. It's important to get an exact match to your car's color, so don't settle on a color that is just close to your car's. Light-colored cars can be difficult to find a perfect color match. Consult an auto paint specialist if you are having difficulty finding the right color. Before touching the chipped area up, it’s important to prevent rust from spreading underneath your touch-up job in the future. Paint on a small amount of rust inhibitor over the chipped area before the primer. Squeeze a dab of primer onto the area if the chip reaches metal. If the chip is surface-level, you can skip this step. Primer is needed for deep chips because regular paint will not adhere to bare metal.  Spread the primer around the small chip with a tiny brush. Only use enough primer for one thin coat. Allow the primer to dry completely. Avoid getting primer on the car paint outside of the chipped area. It will ruin the finish. Apply some of the paint to an area on the car that isn't visible, such as the lip under a door. It is important to make sure the paint you've purchased will not react poorly to your existing paint and also that it matches well. Spread 2 to 3 layers of touch-up paint on the area. The touched-up spot will look elevated above the rest of the paint, which is how it should look.  If the paint chip is on a vertical surface on your car, it’s especially important to wait until the touch-up paint dries between layers so it doesn't run. The painted area should be raised so that it can be sanded down smooth with the rest of the paint job once it is dry. Between each layer let the paint dry for an hour. This will ensure that each layer is set and doesn't get smeared by the next. Also, wait at least 24 hours before continuing the process after you have applied all your layers.
Figure out the exact paint color on your car. Buy a matching touch-up paint color. Apply rust arrestor on the chipped area. Apply primer, if necessary. Test the paint. Apply the touch-up paint to the primed area. Allow drying time between coats and after the layers are applied.