Here you can create, delete and modify labels for quantities added to the graph to specify insulin, carbohydrate or physical activity. If you have already saved some quantities, they will get the label corresponding to their position. So if you give the second position another name, already saved quantities specified with a previous name in the second position will get that name.
To modify a label, touch it.
After Meal, you can select which label stands for the carbohydrate content of meals. For that label in "New amount" in the Left middle menu a Meal button is added, by which you can specify a meal from their ingredients. The carbohydrate sum is than saved under this label and you can later view this meal by selecting the Meal of a saved value.