If you have a teacher who asks the class to call him "Mr. B," it's probably because his name is really hard to pronounce. When you pronounce a word, you sound it out.
When you say something in a particular way, you pronounce it. The verb pronounce has another meaning, too — "to declare formally." It's not too different from announcing something, but it implies something more official and solemn — just think of the phrase "I now pronounce you husband and wife."