To add your card details for billing, you can follow these simple steps:

1. Click on the "Settings" option.

2. Then, select "Billing details" from the menu.

3. Next, click on "Add new card".

4. Enter your card details in the provided fields.

5. Finally, click on the "Save" button to save your card information. By following these steps, you will be able to successfully add your card details for billing purposes.