If a storm devastates your town, it comes pretty close to destroying it. To devastate is to cause destruction to or overwhelm.
Really bad news can devastate a person, or leave them devastated. They are so upset, they feel crushed. A basketball team can devastate an opponent by running roughshod over their defense. The root of the word is the Latin vastare which means to lay waste, which comes from vastus meaning desolate or empty. Imagine a city laid waste after a major earthquake and you've got the picture!