This is a steam water tank, which uses the "steam key". Fill it with water when you use it. Note that it is boiled water (cold or warm water), not raw water. There is a hole in the box, which is hung on the furnace wall. Lift it up and down when you take it out. If you use the "light wave" button, you must take it out, because it is plastic and light wave is barbecue, and all plastics will be cooked under the "barbecue" function. This water tank is only used for "steam function". Usually you can take it off directly without this button. If you want to use it, you have to hang it again. If you use it frequently, clean the box often and don't hang it empty. To steam this thing, just hang up the phone and press the "steam button" and then press the time to start. It is to heat foods that need some water, such as steamed bread and vegetables. Don't hang up if you don't need it. I don't usually need it. Personal preference, some people like to steam things.