Thumbnail & Link to Website Video

While we have been able to share a link to our website, we’ve struggled getting a thumbnail for our all important video to appear when sharing on social media and more despite trying several different things along the way. I’m hoping someone with a lot more technical knowledge than we have might be able to take a look and figure out why. We’d like to be have the video visual shareable but only play on the actual website as it pertains to sales and will create one less step for the customer.
Thanks for any help you can offer.