Facebook retargeting campaigns help engage with past visitors of your website who interacted with your store. This includes viewing products, adding them to your carts, and other important actions from shoppers.
In order to effectively run these ads, you'll need to ensure that you have enough traffic to your store to help build this audience. More importantly, you'll want to ensure the products you've selected to focus your ads on also have enough data/actions.
If you do not have enough data to run Facebook Ads, you can always start Google Product Listings or Google Shopping ads to get extra traffic to your products. This will help kick-start your Facebook ads to get the best results!