Difference between Image preview and preview image set?

Hi all, Total newbie here. getting ready to upload and wonder what is the difference between the Image preview upload and preview image set upload field? Thanks.

image preview is the one that will appear on item’s page directly (and also top of that 590px image preview is will be shown in envato item search pages). Preview image set is the one that images section that opens when clicked. You can add mockups of your design etc.That is optional you can use it or not, up to you. You may notice some items image previews’ are clickable some of them not. This is why. Hope it is helpful

Thank you that helps immensely!