Need help, new seller starting.

Hi guys, I’ve just started with Amazon selling, went through all video on academy but still there is some things I can’t understand. After I add a product to sell, why does it shows on my inventory as “inactive (out of stock)”.like I know it is saying out of stock but the produced I added was already listed on Amazon. Wasn’t they supposed to have this product to deliver if it is in the website? Thanks for the help in advance