Simmering and sautéing are two different cooking techniques that are used to prepare food.
Simmering refers to cooking food in liquid that is just below boiling point. The temperature of a simmer is between 180-190°F (82-88°C) and it is characterized by small bubbles that rise to the surface of the liquid. It is mostly used for dishes that require a longer cooking time, like stews, soups, and braises.
Sautéing, on the other hand, refers to cooking food quickly in a small amount of hot fat, usually oil or butter. The temperature of sautéing is between 350-450°F (175-232°C) and it is characterized by the food being cooked quickly and constantly being stirred or tossed. It is mostly used for dishes that require a shorter cooking time, like vegetables, meat and fish.
Therefore, simmering is a gentle cooking method that uses a low heat and liquid to cook food slowly over time, while sautéing is a high heat, dry method where food is cooked quickly by stirring or tossing in a small amount of hot fat.