Hi Woogon,
First you can do that ONLY if you use PayPa,l because DNN support only PayPal as payment gateway for the recurring role payment!
You have to configure your portal to support payment subscriptions (Admin > Site settings > Advanced Settings > Payment Settings). Select your currency, select 'PayPal' as Payment Processor (the only one), enter your PayPal email account in the Processor UserId, DO NOT enter your PayPal account password in the Processor Password field, save your portal settings.
Now you have to define the fee for the 'subscription role(s)' you want to sell from the Store module. Go to Admin > Security Roles then select an existing role or create a new one. Expand Advanced Settings (this section is displayed ONLY if you have defined a PayPal account for your portal), enter an amount in the Service Fee, enter a Billing Period and select a period (Day(s), Month(s), ...), update your role.
Now you have to map a Store product to the corresponding 'subscription role(s)', go to the Store Catalog module, select an existing product or create a new one, select the 'subscrition role' in the Apply Role setting, save your product.
Gilles