The # symbol, called a hashtag in Twitter, is used to mark keywords or topics in a Tweet. It was created organically by Twitter users as a way to categorize messages. A hashtag is a way to bring together Tweets on the same subject. It is simply a way for people to search for tweets that have a common topic.
1) People use the hashtag symbol # before relevant keywords in their Tweet to categorize those Tweets to show more easily in Twitter Search.
2) Clicking on a hashtagged word in any message shows you all other Tweets in that specific category.
3) Hashtags can occur anywhere in the Tweet.
4) They can be conversational or commentary. I personally love to use them for an event. Last year I won a small award for being one of the top 10 Tweeters at the InfusionCon 2011. It was all done using a hastag.
If you want your target market to be able to easily find you, be sure to use hashtags for your keywords in your Tweets!