Washing soda is often confused with baking soda but it's quite different. For starters, you don't bake with it! It's not edible. It is great as a laundry additive, to boost the cleaning of your detergent.
You can make an effective scouring powder out of washing soda and baking soda. Mix 1/4 cup washing soda with 1 cup baking soda and use it as you would Comet or Ajax scouring powder. Washing soda can be purchased in the laundry aisle of your local grocery store.
Washing Soda is sodium carbonate and can be found in the laundry section of the grocery store. Washing soda cuts grease and removes stains, disinfects, and softens water. If you can't find washing soda you can substitute baking soda (sodium bicarbonate) but they are different. Arm and Hammer sells both Washing and Baking Soda. (Never use washing soda for baking!)
This is a page about buying washing soda. Washing soda is primarily used for cleaning laundry but it can be used for other cleaning tasks around the house.