Hashtags help to organize posts and connect like-minded conversations on tools like twitter and Instagram. Simply put, a hashtag is made of the # symbol and a word or phrase, no spaces and usually no punctuation.
Here is a concise podcast from Mark Barnes, explaining Twitter Hashtags
Hashtags to Explore
For the most complete resource on Twitter hashtags, twitter edu chats, and suggestions on who to follow when you are getting started, see Cybraryman!
Have people follow you on Twitter via text messages (must have tweets set to public.):
Message: follow @username