You can assign product images to products both from the website media gallery and from external source.
The product image column in the file is the second one (the first one is product ID).
Place the image URL in the file field in the product row second column. Example image URL:
Product Images from external source
If you provide the external URL in the CSV file, the image will be imported to WordPress media gallery and assigned to the product.
Import multiple product images
If you also have Product Gallery Advanced active you will be able to assign multiple images to one product. Use a list of comma separated URLs to achieve that.
Multi image data format example:
The best way to figure out the CSV file data format is to export the products first. The import and export format is always the same.