Hashtag – A hashtag is a word (any word) beginning with the # sign. (Example: #writer)
It’s a way to categorize messages to help them show more easily in Twitter search. Hashtags can be used or organise conversations around a particular topic, to group folks, target folks, and meet others with similar interests. When you click on a hashtag you are taken to a group of tags associated with that term.
– A retweet is someone else’s tweet that you choose to share with your followers. Use hit the retweet’s button to send the original text or image to all of your adoring followers.

Mention – To bring a tweet to someone’s attention and still allow all of your followers to see the message, use the @ key followed by the username. Example: @username
All mentions are clickable and link back to the profile of the person or business mentioned.

Reply – To respond to a Tweet, hit the reply button. When you reply, your response is public to everyone and it will show up on your timeline of the person whom you are responding to. If you want your message to be private you can send a direct message where only you and the person you’re messaging can see. Private messages can only be sent to someone you are following and who follows you back.