Open the product in Shopify.
Scroll down to Variants and click on ‘Add variant’.
Type in the Option name, such as size or color.
DO NOT add spaces to option names within Shopify, it will cause the variations widget to not work.
Type in the option values. Separate each value with a comma.
If desired, you can change the price of the different variants. You can also choose to add an image for each variant. If you don’t add an image for each variant, then the image that you have uploaded for the product will display in the cart.
Copy the product number. If you do not know where to find your product number then see this article.
Open your Muse file. Grab the Item variations widget. Paste in the product id and type in the option name. Note that the option name is case sensitive so type it exactly the way that you typed it in Shopify.