Twitter hashtags can be very confusing especially for people who are new to Twitter. In a nutshell, a hashtag is any string of characters excluding spaces that follow a number sign (e.g. #cool or #whataretheytalkingabout).
Who creates them? Anyone can create a hashtag.
What is the purpose of hashtags? To categorize key words or phrases which can be easily found in a Twitter Search.
What do they mean? Clicking on a hashtagged word displays all other Tweets marked with that keyword. A popular hashtagged word usually becomes a Trending Topic.
Now that you have a better sense of what a Twitter hashtag is, I encourage you to try creating a hashtag with your next Tweet!