iMac <-> iPhone sync (iMessage)

Hey guys,

I got my new 27'' iMac last week and I love this computer so much!
But I have a question about iMessage.
How can I sync my Mac-iMessage and iPhone with iCloud? If I write something in iMessage on my iPhone it doesn't sync with my Mac.
There are a few accounts "iMessage", my email, Bonjour and I don't know how it works.

Please help . Thanks!

Now it works, but it's very buggy. Every contact is now 10x in my list and if i want to open my contact list on the mac, the app crashes...