You can enable the Facebook Shop function by adding products to Facebook manually or via a feed from your ecommerce platform. Once you have products listed on Facebook, the Facebook Shop is enabled and you can point the Shop button to your Facebook Shop instead of a website. We have an article that explains how to do this (it’s under Step 4). If you haven’t listed products yet, this article also shows you how to set up a Facebook Shop and covers your product listing options. That should cover everything you need to know to set up your Shop.
Shopify, Ecwid, and BigCommerce are three top ecommerce platforms that integrate a product feed directly with Facebook Shop, but others do too. If yours doesn’t, you can use a plugin like StoreYa Facebook Store plugin. Again, you can also add products to a Facebook Shop manually, but if you have a number of items, the feed option is the way to go.
I hope this information and our Facebook Shop article points you in the right direction.