Please follow the our guide “WooCommerce Product with a Swatch” to see how to add the product and its variations into WooCommerce. Step 2 of this guide and the adding of the swatch colours / images can be ignored as this is not relevant for items without a SKU.
Once the variations are added to the website, and configured with pricing, you will need to use the parent variable stock item SKU rather then the child items SKUs as these do not exist.