While you may not have heard of Twitter personally, there’s a good chance that one of your friends has and uses it regularly. Or your doctor, optician or even close relative. The truth is, while it’s not quite mainstream yet, Twitter is fast becoming one of the more popular online networks around.

Yet there are still a lot of questions being asked about what Twitter is and why it’s taking off the way it is. This, then, is a layman’s introduction to the service.

It’s Good to Talk

At its most basic, Twitter is a way to let you have a conversation with other users, and keep them updated to your current status. The welcome screen for Twitter even asks, “What are you doing?”

To keep things simple, Twitter only allows you 140 characters to get your message across. While this might seem small, it’s surprisingly effective and makes sure that messages are punchier as a result.

There are two message options on Twitter – public ( tweets) and private (Direct Messages, or DM’s). The public tweets can be seen by either anyone who is following your updates, or people that you have directed the message to, using the @ syntax.

So Why Sign Up?

Although there are no complete figures collected for the numbers using Twitter, guesstimates put it at around 5-6 million users. This is small compared to Facebook’s 150-million plus members, yet for such a relatively new web app, it’s a decent amount. And interest is growing all the time, with celebrities joining every day.

 So why should you be interested?

When you have a SMS text message conversation, or Instant Messenger chat, you know how instant that can be. It offers a quick and simple way to speak to someone and can save the bind of having to wade through emails to remember a topic.

Twitter is the same. Just transplant the SMS or IM conversation into the Twitter stream and you have the same quick and easy way of chatting with people. The difference is here you can potentially chat to another 5-6 million people.

If you need information on something quick, or directions to a place, Twitter users offer that to each other. If there’s an emergency, Twitter users in the area keep others up-to-date with what’s happening.

So it’s not only a great conversation tool for meeting new friends and people that share your views – it’s an information portal for all that’s currently going on in the world. It’s also a great business networking platform, but that’s a topic for another post.

So, to paraphrase Twitter’s own message – “What are you waiting for?”