You will need to upload two files:

1. the image file, this will be the image shown on the sidebar. Image can be a normal jpg file or animated gif file, i recomment to keep it within resolution of 300x250 (similar with most affiliate image link)

2. the downloadable content, be it ebook or any resources you are offering.

Go to Dashboard > Library > Add New to upload both files,

Remember to copy the urls for use later