Congratulations on being chosen to sell on Walmart, that’s a big step. SKU numbers are the numbers you create to track your products internally. Here’s an article explaining SKU numbers and how to set them up for your products and business. UPC codes are a registered universal number that you need to acquire from the GS1 website, which is the international governing body for the UPC code system. It sounds very formal, but the process is easy. Learn about that in our UPC barcode article.
These two articles should explain everything you need to know to get these numbers for your Walmart product listings. Good luck!