There is a scheduler running daily, checking the status of the subscriptions (not in state 'draft' or 'cancelled / closed'.) and the 'generate next invoice' date. if this day comes, a draft invoice is created. 

The scheduler can be found in Settings - Technical - Scheduled actions and in V13 called: 

Sale Subscription: generate recurring invoices and payments

Hello Angelica!

Thank you for your question.

As covered in the Subscription Basics video, the way the invoices are handled is set in the Subscription Templates, with the Payment Mode field.

So, once your subscription product is correctly configured, you can sell it on your eCommerce, for example. There, your customers can pay with a credit card or the payment method of their choice. Once the payment is confirmed, a subscription is created automatically and will keep creating invoices and make payments according to what you have set in the subscription template.

If you want more explanations about the way invoices are handled in Odoo, you can have a look at the Invoicing and Accounting chapters.

I hope this helps :)

Cheers,
Jonathan