Outbox vs Sent Items, what's the diff

I'm perplexed with Outbox and and Sent Items when you view your personal messages section of the forum.

Have I sent something in the Outbox?
If I haven't how do it I do it?

I ask because when using "Submit" it only sends it to my Outbox, not Sent Items, which seems to be an a bezare why to do things?

I guess, my biggest question is, have I sent the message to the person I need to?

 

Ah thank you ^.^