How to Use the Number Sign on Twitter
While reading tweets from other Twitter users, you may have noticed them using the "#" symbol. This is what is known as a hashtag, a marker used to categorize tweets. Hashtags help Twitter users find tweets related to a specific topic.
Type out a tweet as you normally would, but don't submit it.
Think of a few keywords for your tweet. It's suggested not to use more than three hashtags in a single tweet. For example, if you were composing a tweet about the pancakes you ate this morning, you may use the keywords "breakfast," "food" and "pancakes."
Add your hashtags to the end of the tweet in the format "#keyword." You can also place hashtags in other places in your tweet's text if you would like. For example, the following tweet could be found by users searching for "#example" and "#howto":"This is an #example tweet. #howto"
Submit your tweet. Other users will be able to find your tweet by searching for its hashtags, or click on the hashtags in your tweet to find related tweets.