Long ago, before microwave ovens, blanching or steaming vegetables used to involve big pots of boiling water on the stove. While that is still a popular method for many cooks, I find it more convenient to steam my vegetables in the microwave. Much less water is required this way, which not only preserves water but also might keep vitamins and other nutrients from "boiling out".
To steam vegetables in the microwave:
Rinse vegetables well and cut up as desired.
Place the vegetables in a deep microwave-safe baking dish. Add enough water to make a shallow layer on the bottom of the dish.
Cover and microwave on high until done.
Note on blanching:
To blanch vegetables (prior to freezing or further cooking in a recipe), microwave just for a minute or two, until crisp-tender but not fully cooked.