Hashtags are keywords and are a way of tracking topics on Twitter. By using hashtags, you can help people who are looking for more information on your subject find your Tweets.
You add hashtags to your tweets by using the hash symbol, #, and a word that defines the tweet's topic. For example, #election or #G20. You can include more than one hashtag in your tweet, if appropriate.
Anyone can create a hashtag, there isn’t a central place that creates them, groups of people just start using them.
Link sharing is great on Twitter. If you want to share a link, copy the link from the search bar at the top of your browser and paste it into the tweet. It won’t work as a link unless it’s preceded by http://
If the link is really long, put it into a url shortening site like: http://tinyurl.com – this will give you more space for your accompanying comment.