Washers and dryers are located near the pools at OKW (unless you get a one bedroom or larger - then they are in your villa). They are free. Each laundry room has maybe two washers and four dryers. There are vending machines with single load detergent. Or they might have it in larger sizes in the store. Or you can bring your own/buy it from a grocery store off the Disney property.
You have to stay with your laundry - that is, hang out at the pool or trot back and forth between your villa and the laundry room to get your clothes out of the washer and dryer as you complete each load. With so few washers and dryers, it's a big inconvenience to others to arrive and find clothes finished in the washer, dryer empty. Or clothes in the dryer, not spinning, just sitting there. Many people will unload your stuff, lay it wherever they can find space and do their laundry.
Finding a vacant machine is the luck of the draw.