how do you send messages on Twitter?

[LexiSan]

Personal messages are called "direct messages." They are private and no one can see them but you and the person you sent it to.

All you have to do is type:
d username message

in the update field.

The d tells twitter that is a direct message and the username tells twitter who to send it to.

You can also just click the "Direct Messages" link in the right side bar of your homepage and do it from there.

However, you can't send a direct message to someone if you're not following each other. This is to prevent spam and such.

You can also do @reply username in the update field, but these messages are public and can be seen by everyone.

I hope that helps :].