Small chips and blemishes are best repaired with a can of touch-in paint and a brush. For larger jobs, use an aerosol spray. If possible, work in a dry, warm, dustless but well ventilated atmosphere.
The best way to treat a dent is to raise the metal almost to its original level, then to level the surface with a thin layer of plastic body filler. You can do this with most of the plastic filler kits available.