People use the hashtag symbol (#) before a relevant keyword or phrase in their Tweet to categorize those Tweets and help them show more easily in Twitter Search. If you Tweet with a hashtag on a public account, anyone who does a search for that hashtag may find your Tweet.
The hashtag is a favourite tool of conferences and event organizers, but it's also a way for Twitter users to organize themselves. It is one of the most complex feature of Twitter for new users to understand.
So here is an Infographic by Social Caffeine on everything you need to know about Twitter #tags:
Featured Image By: danielmoyle