Nearly 3 million successful sellers are selling on Amazon in 2020. The main differentiator among Amazon sellers is the method of fulfillment they Fulfillment by Amazon (FBA) and/or Fulfillment By Merchant(FBM).
Fulfillment By Amazon (FBA): A distribution process on Amazon in which a vendor sends their goods directly to Amazon's warehouses. Then Amazon stocks the product and delivers it to the customer directly. They also manage customer service.
Fulfillment by Merchant (FBM): A distribution system on Amazon where a vendor lists their goods on Amazon but handles all stock, shipping, and customer service by themselves.
To know about the comparison between the two read the full article.