Yeah that's right, we Belgians make the best chocolate ~3~
Costco is a retail-store that sells wide variety of goods (like food, clothing, some electronics, etc.) much like Walmart. The difference to Walmart is they sell some of their food in bulk-packaged (you can save money by buying them in bulk). Unlike Walmart, you need membership to shop in Costco (it's only $60 a year).
Kirkland-Signature is a trademarked-product-brand of Costco (Costco source products from manufacturers and retail them under the Kirkland-Signature-brand).