Welcome to the Shopify Community! I'm not exactly sure what you mean by design a product? Are you able to please explain what you are looking to do in more detail? Any examples, or screenshots you can share about what you are trying to achieve, or where you are getting stuck would be very helpful for understanding.
That being said, I'll share some general help documents with you that will be helpful if you're just getting started with Shopify:
Once I have more details about what you are trying to achieve, I'd be happy to assist further. Thanks!