In General Options tab, enter your email and password of your game portable account. Then press start trial button.
Change to Worlds & Castles tab, press refresh button to load worlds and castles for your account.
If no wordls are shown, check your account data on http://lordsandknights.com/
Here tells you how to make your portable account: http://support.xyrality.com/index.php?/Knowledgebase/Article/View/23/7/making-your-account-portable