Tweets are the building blocks of your communications on Twitter.
You’ll be surprised by how much you can say with 140 characters or less.
A hashtag is any word beginning with the # sign. People use hashtags to
organize conversations around a specific topic. Clicking on a hashtag takes you
to search results for that term.
Sometimes you want to bring a Tweet to someone’s attention, but you still want
all of your followers to see the message. So instead of a reply, use a mention.
Include the @username of whomever you want to mention in your Tweet, and it
will appear in the Mentions section (in the Connect tab). All @username mentions
are clickable and link back to the mentioned individual’s profile.
You can respond to a Tweet by hitting the reply button. When you reply, your
response is public, and will show up in your home timeline and the timeline of the
person to whom you are responding. The reply will also be visible in the home
timelines of people who follow both you and the person to whom you sent the
reply. Meaning, someone not in the conversation has to follow both of the people
replying to be able to read both sides of the conversation.
You can pass along someone’s Tweet by retweeting it. Just hit the retweet button
to send the original message to all of your followers.
Twitter’s link-shortening feature allows you to paste a link of any length into the
Tweet box and it will automatically be shortened to 19 characters. This makes it
easier to fit long URLs into the 140 character limit.
From American Express Smallbiz