Tare is a feature on the weight scale that allows you to have a net value excluded of the weight of bowl which you are using to measure food.
If you set the tare to the bowl placed on the food scale it means food scale will show zero net reading. But when you put some food in the bowl, it will show only the reading of food, not of the bowl. This helps in having the exact measurement of food without any inconvenience of manual editing.
The zero, without tare, means there is nothing placed on the food scale therefore it is zero, but zero with tare means we are excluding the weight of thing placed on the food scale.