A countertop dishwasher washes dishes the same way traditional models do, by spraying streams of water on dishes in combination with detergent designed to tackle food and grease. You should never use regular dishwashing detergent in any dishwasher as it creates too many suds.
The water supply for a countertop dishwasher comes from your kitchen faucet. Some models require you to turn the hot water on directly, while others have a built-in heating element to heat the water. You also need to plug the dishwasher into a power outlet.
Countertop dishwashers vary in size. Some resemble large microwaves. Though countertop dishwashers have many of the same features as regular dishwashers, there are size limits to what they can wash. You may have to hand wash larger plates and platters.
Countertop dishwashers are not created equal. Some operate with three cycles while others have five. If you're looking for an energy efficient dishwasher, you can purchase a model that washes your dishes, but doesn't dry.