Trying to sync address book with icloud

I have been using the Address Book on my MacBook to organise all of my contacts and put them into groups. Now I want to sync all of these groups with my iCloud so that I can access them from iCloud as well as on my MacBook. How do I do this? Whenever I enter my iCloud password in Address Book two errors come up. One says Server Not Found and the other says The account "iCloud" is offline. No syncronisation will take place with the server. Click this icon to change to "online". I have clicked the icon but nothing happens.