From the Role Center, navigate to the Subscription Batch.
Use the New action on that list page to create a new batch. Note: If your setup has more than one subscription type, you will be asked for a subscription type to run the process for (the monthly charged billing, the quarterly one, and so on). The selected subscription type contains the information on what period you are billing.
The process will then create all the charge entries based on currently active memberships. Note: The invoices are not created until the batch has been posted and the access settings per member have been updated.