Cathy, fixing the hole in your door is the easy part, refinishing is the hard part. For about a half inch hole in a hollow core door, use Minwax Wood Filler or Bondo like you would spackle on a hole in drywall. If the hole was bigger, you would want to put something behind it but you should be OK if the hole is that small. You might need to put 2 layers on. Overfill and sand flush.
If the door is painted, you got it made. Bondo works well and can be spot painted after a couple of hours. If the door is luan or other wood, I would use the Minwax Wood Filler and you will have to stain and maybe use tone spray to get the repair to blend in. The Minwax stain pens (like Magic Markers) can help you with this and you will want to use a couple of colors probably. If your door is finished, you will want to spray on clear polyurethane or lacquer. I can't be any more specific about this as there are so many possible woods, finishes and combinations. Henry