How do I use twitter.com to contact and tweet newstation people?

Question: I have joined twitter.com and I hear a lot of news station anchors say that they have been "twittered" or "tweeted" by a member of the public with their comments. I can't find any way to do this. The way it looks to me is that all you can do with Twitter is to say in 140 characters what you are doing today - so what is its purpose? Sorry - 2 questions. I would love some help with this.

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