We already told you several times what the product_parent_id is ! It's even written in Eliot's post above:
You will have to specify in the product_parent_id column the product_code of the main product
And the example CSV:
product_code,product_parent_id,size
main_product,,big
first_variant,main_product,big
second_variant,main_product,small
So if you have a main product with the code "main_product", its variants must have the value "main_product" in the product_parent_id.
If "nothing happens" it means that you didn't import the shipping prices properly. Please check that you can see them in the product edition page, in the shipping prices area and that all their data is correct.
Variant prices do NOT auto add to product prices. Variant prices replace the main product price. If you have a "price_value" column in your CSV, you can specify the price of each variant of the price, so you could simply enter there the price of your main product+the variant price.
PS: please stop posting the same questions everywhere or we'll have to delete doublons.