The maximum limit for a Tweet is only 140 characters. This includes all characters and spaces. It is acceptable to use slang and abbreviations in your Tweets.
Followers are those who follow you and read your Tweets. The only ones who see your Tweets are your followers unless you have been retweeted or searched.
Those following you will see all of your Tweets in their Twitter stream (the list showing all the Tweets).
# means hashtag. The hashtag is the subject of your Tweet. You can include a hashtag to make your Tweets easier to search by others. Here is a great list of educational hashtags by Cybraryman.
@ means a specific person. If you are talking to that person, the @ is at the beginning. If you are talking about that person, the @ is located in the Tweet.
RT means retweet. You are simply repeating what someone says.
MT means modified Tweet. If you want to use only part of a person’s Tweets, you included MT.
My Twitter handle (username) is @WhiteheadsClass. I would love to have you as a follower.