The front cover is essentially an advertisement and it is particularly important to get it just right for stories published only in the e-book format.
It is all about getting that click.
The cover must stand out even at thumbnail size to stop potential buyers from scrolling past and entice them into clicking on your book to read more.
Covers are always delivered in triplicate; as jpg, pdf, and png files. This is to facilitate your using the image for many different purposes and sites. Some printers and publishing platforms ask for pdfs, while others use jpgs. A smaller png is perfect to have on hand for your thumbnails.
Social media banners are a great way of featuring your work at the top of your social media platforms. Included in this package are two png files, sized to fit two different social media platforms of your choice, e.g. Twitter and Facbook. Social media banners can either display your book's details or highlight a special event like a sale, a book signing, or a blog tour.