A: AST user ID and password: You need to use the same user ID when you used to sync your MWS account with ASellerTool.
B: Amazon seller ID: If you are a US seller, use ATVPDKIKX0DER as Marketplace ID. You can find your seller account ID here.
C: Fulfillment Channel: Choose to list your items as FBA or MF. You can switch between them. E.g. If it is set to FBA, but you want to list following items as MF. You can change it to MF, then start to list those items as MF. After you finish, you can change it back to FBA.
D: Box Content (FBA only): If you ship everything in one box, you can skip it. If you ship multiple boxes in a shipment, Amazon requires you to provide box content information for each box. You can choose to use the 2D barcode to show box content.
E: Ship-from address (FBA only): Specify the address where you ship the FBA items from.
F: Transfer Between Computers: Click “Export” to backup your settings and work into a file. Click “Import” to retrieve your backup. The backup file is also where we can help you troubleshoot.