Enable the Contacts service from the Services tab in the Ubuntu One Control Panel.
Click Applications in the Launcher and find Evolution Mail and Calendar. Once open, click the Contacts button at the lower left. Click to select your Personal address book from the list on the left. Open the Actions menu at the top and select Copy All Contacts To... from the list of options. Select Ubuntu One and click OK. From this moment, all your contacts in Evolution will be synchronized with your Ubuntu One cloud as well as to any other devices connected to the same account.
To make the Ubuntu One synced address book the default address book in Evolution, again click the Contacts button at the lower left of Evolution Mail and Calendar. Click to select the Ubuntu One address book from the list on the left. Open the Actions menu at the top and select Address Book Properties. In the window that pops up, mark the check box next to Mark as default address book and click OK.
You can also create, view, edit, and delete contacts from the web interface.