Hello Carine.
You can import multiple product images separating them with semicolon or comma, for example:
"http://imagehost.com/image1895.jpg;http://imagehost.com/image1896.jpg"
Also please find more details on how to import product images in the articles below:
http://www.prestashopmanager.com/useful-articles/prestashop-product-management/how-to-import-prestashop-images-from-urls/