You should not be sending inventory to amazon if you don't understand such a basic thing. I would put your account on vacation and do a lot more studying first. You should also start with selling FBM to know if your product will be successful before you commit your inventory to their warehouses. Lots of posts on here about all the ways that FBA goes wrong that you should read over. And all the extra costs you incur, from missing inventory to storage fees to low inventory fees.