Each product has a limit of 100 variants.
If a product has more than 100 variants, they will be removed automatically during the import.
Each product can have up to 3 options (attributes). The options can be different from product to product. For example, one product can use size, color, and material, and another product can use weight, finish, and ships from.
Read more HERE.
If you have less than 3 attributes there is an option 'Add attribute': enter name and value of this attribute -> click 'Apply'.
You can also 'Add variant':
and 'Reorder' them: click and drag an option name to move it to a different position. When a customer is on the product page, they see the options for this product in the order that you set.