I actually went on a short course to learn twitter!
I'm still getting to grips with it, but a few pointers I have learnt along the way:
Set up your account (@something) and add a picture (doesn't have to be a picture of you) as no one likes to talk to an egg (the default picture).
You can then 'follow' different people or accounts. My first mistake was to follow the BBC News who post a 'tweet' (a message) every two minutes which meant that I never saw anyone elses' tweets.
I would thoroughly recommed following @westendproducer and @auditionpianist as they are so funny!
You can also follow your favourite pop stars, west end stars and your accountant!
Eventually people will start to 'follow' you and then they will read the messages you post.
If they follow a lot of tweeps (people who tweet!) they may not read all your posts as a timeline (the list of messages like on FB) usually only holds around 100 messages.
If you want to reply to a tweet then you hit the 'reply' button and your reply will be seen by people who follow you and the person you are replying to (but in public).
If you want to send a private message ( a DM) you can only do this if you are both following each other.
The messages themselves can only be 140 characters. There are applications which add a longer message as a file, but I don't know how these work yet (I'm still learning!)
As with most things in life, it's not the quantity (of followers) but the quality which counts. Better to have 50 lovely people following you than 1000 spam type people.
Twitter can be done on a pc, but I personally find it easier to use on my iPhone.
Perhaps another twitter user could explain about the use of hashtags (#) as I'm still getting to grips with this side of it!
It can be quite fun and addictive when you get going (a lot like this forum!).
Let us know how you all get on!