Hello @gbrachetta,

Hope you are doing great. Your featured images should be at least 750x375px (just like on the demo).

You may also want to add some widgets to the Right Sidebar, so the blog page look similar to the demo one.

To add banner to your Blog Page, you should simply add some HTML code to the index.php file. I believe lines between 15 and 23 are good place to paste your code.

Thank you,
Piotrek