If you look in the forward closet, there will be a panel against the back wall. If you remove the screws and pull that panel off, you will find an electrical outlet, a hot and cold fawcett along with a drain pipe. The black drain pipe drains into your grey tank.
This is pretty much everything needed you'll need to install the washer/dryer. If your dryer requires a vent, then you will have to have a hole drilled into the outside wall, to install the dryer vent. If it's a ventless dryer, then there is no need to drill.