A rice cooker is not necessary to cook rice in a microwave. Microwave rice cookers are available, however, for those who wish to use them.
To cook plain rice in the microwave without a rice cooker, put the rice in a microwave-safe bowl and microwave on high for 10 minutes or medium-high for 15 minutes. Be sure to use a bowl large enough to allow the rice to expand during cooking. Let the rice cook the entire time without interrupting to stir. When the rice is done, remove it from the microwave, season with salt, and fluff with a fork.