Help with Private Messaging

What is the difference between the Outbox and the Sent Box?

The outbox is for messages that have been saved and not yet sent.

The sent box is for messages that have already been sent.

That's what I thought. Now, how do I actually "send" a message in my Outbox?

It HAS ALREADY BEEN SENT. Do nothing!

When it sits in your OUTBOX...it hasn't been picked up yet.