The Washing Machine is an appliance which allows you to repair your armor, eg a Chestplate. To power the machine, you need to put Soapy Water or Super Soapy Water in the top right slot. Simply put your armor into the corresponding slots on the GUI and hit the start button. Depending on the fuel you use, after every X amount of second(s), it will add one durability back onto your armor.
You can use the RecipeAPI to register custom armor from other mods to work with the Washing Machine.
Crafting Recipe Edit
7 blocks of quartz, 1 glass pane 1 furnace. Place quartz blocks across the top row, middle left, middle right, bottom left, and bottom right. Then place a glass pane in the exact middle, and a furnace on the bottom middle.