The lids on modern rice-cookers are hinged to the body, while older models have saucepan-lid types covers.
Modern rice cookers all use microchips to control the cooking process. To cook white rice, the rice is measured (say 2 cups) and rinsed, then added to the inner pot. Then cold water is added up to the white-rice line (in this case the 2 cup line.) There will be another scale for brown rice (as more water is required) or for cooking other things in the appliance.
Then the lid is closed, and the rice cooker does the rest, nowadays giving a countdown in minutes to the "ready time," and beeping when done.
Rice cookers are also able to keep rice warm safely for up to 24 hours. This helps to avoid the dangers of food poisoning due to Bacillus cereus.
Rice cookers, when purchased, normally include a small "cup" measure and a plastic paddle for doling out the cooked rice.