The interior is self-cleaning. If a stain does occur, clean with dishwasher detergent and water, wearing rubber gloves to protect hands from very alkaline detergent. A heavy film buildup from hard water minerals may be removed by adding vinegar or citric acid crystals (buy at drugstore) to dishwasher without any dishes in it, after it fills with water at start of first cycle. Do this only if appliance manual suggests this is ok, and if the buildup bothers the owner (as it does no harm).
However, very hard water can deposit mineral film on dishes, glasses, and flatware, and on dishwasher pump and moving parts; it is wise if water if very hard to install
a water softener before installing a dishwasher.

If iron in water causes rust stains inside dishwasher, buy a commercial soluble rust remover (grocery or hardware), checking label to be sure it can be used to dishwasher. Start empty dishwasher on rinse cycle. As it fills, open and add 1/2 cup rust remover. Let dishwasher complete cycle. If iron problem continues so that another treatment is required, better to install
an iron filter in water system to remove iron as this will affect dishes, laundry, and all fixtures.