Well, sort-of round with a dimple at the top and a little stem. The apple might be upside-down or sideways. You must look for stems in all directions. Forget about stems. Let's start with color.
Most apples are red, but then again some are green.
I guess a bad apple might even be brown. Apples are other things too. For example, most apples are a little bit shiny. They reflect light well, but not as well as a mirror. A mirror is something that shows an image of you and what's behind you when you look into it.