Cooktops are used to cook food, and are usually the final stage with meal preparation.
Sims can either have a meal or serve a meal. Having a meal creates one meal, while serving creates six servings of a meal.
Grilled food can only be made on grills, so you won't be able to make hot dogs with stoves. Also, all grilled meals are only available in multiple servings, rather than just one.
Stoves get dirty and can be cleaned, which increases the Cleaning skill.