To feature a product, simply select "Edit" from the Actions dropdown.
You'll arrive at the same page that you were on when you were listing your product.
Scroll down to the Item Details section, and at the bottom of that you'll see a toggle where you can feature the product.
It's important to note: If you turn this on whilst creating a new product, and you save the product as a "Draft", it will turn this feature toggle off.
Once you have published your product, you can return to this page via the steps outlined above to turn it on and feature this product.