This video is very helpful.
Fulfillment by Amazon (FBA) is a way for sellers to ship their products directly to an Amazon warehouse. Amazon will handle the sale, picking the product from inventory, shipping, customer service, and returns. Amazon FBA fees range from 45 cents to $1.35 per unit, and $39.99 per month for a Professional account. https://fitsmallbusiness.com/fulfillment-by-amazon/