What should I do to continue using Casual when the trial period is over?

All you have to do is choose the pricing plan that suits your needs best once the trial period is over. After that, you can subscribe to Casual by clicking on one of the subscription buttons in the app:

• Find the Subscribe Now! button in the Casual app header. 
• Click on your name in the app's header and select My Subscription.

Then you’ll be redirected to the Subscription Management page. Simply pick your pricing plan and finalize your subscription.