Cloning a variant is useful when you need to add a variant very similar to one that had already been created.
When you clone the variant, it first creates a new variant with the exact details as the cloned variant.
You can edit the variant details, and create a new variant.
Click on the "Clone" button on your product page:
A new row will appear with the details of the cloned variant. Make the necessary changes to the new variant.
When you are done, enter the stock quantity. Click on Save variants.
Your new variant is now available and ready to be sold!