How does Twitter work?

[cheryleene <3]

@USERNAME is like writing 'to' on a letter; it starts the message when it's the first word in it. But, if it's in the message, it just links to the person's twitter account.
RT, or ReTweet, is basically sharing what someone wrote by showing it on your account. So if person A were to tweet 'Hi' and person B clicked on ReTweet, then it would show up on their profile and be shared with their followers.
About __ hours ago just shows what time it was submitted, and via ___ is where it was tweeted from; there's a lot of sites like TwitPic that are used as applications.. You use them to Tweet on another site.