How can I sync email messages and contacts from iMac to iPod?

I don't understand the iCloud thing, I thought when I set that up it would show my "sent" and "inbox" etc on both my iPod and iMac~ but it still only shows what I did on iPod or what i did on iMac.

I want to be able to see what I've sent and received from my iPod to also show on my iMac and vice-versa.