Storewide notifications report on all products and variants in your store. They are the simplest type of notification.
Collection notifications report on all products in the Shopify collections you select.
Product / variant notifications report on only the products and variants you select.
CSV notifications allow you to upload a CSV file containing your selection of variants along with their desired low stock thresholds. These are useful for stores with large amounts of variants or in cases where you want to set different thresholds for different variants.