Getting order details from commerce modules

hi to all i want access order details placed by commerce module in my custom module . so that on the basis of that i can send email to customer. for example
As a user, after order is completed, I will get a text email with detailed information about my order. and if order is paid user get email order is paid. and if order is place but payment is not done i can send email to customer to remember the payment after 3 days. like this after 3o days .