Hello and welcome to Android Forums. Hopefully I can help you with your problem.
You need to contact your carrier. They can walk you through the steps needed to add money/minutes. Without knowing your service provider, I cannot answer your question with step by step instructions. Your carrier will be more than happy to help you add money/minutes.
If you have any other questions regarding your device, I invite you to join Android Forums. We have many sections for specific devices which contain a wealth of information.