Scrum roles and responsibilities

Hi all, I am a team member as a developer and we are using scrum. My main issue are the roles and responsibilities. 

The scenario of the issue that the sprint backlog has one thing. That thing is to add a new tab on website and let user to choose one of payment types.

These types  are credit card and bank account. And the user has to choose only one of the payment types. We can create many subtask(add tab, fetch credit card info, fetch bank account info, save the choose of the payment type..etc).