FBM seller in Canada , first time uploading any product, cannot finish the process.

I have found a protein powder that sells at wal mart for significantly less than other variations of the same protein powder, same size , but different flavors , on amazon. I have never uploaded any product to my amazon seller account. I physically have 1 unit of this product. I search for the product and this flavor is NOT on amazon already. I am attempting to add the product ID, and am using the barcode numbers listed on the product. I’m not sure if this is what i should be using. Every time I think i’m done the process there is something else to add, or some other road bump. I am unclear if this product is up and available on my account. Every video I watch is very assumptive “It’s as simple as adding this or that” ….no it’s not. Any clear direction or advice will help. Thanks.