Translation:Our cafeteria bought four kilograms of cookies.
Yes, British "biscuits" = American "cookies". And just to confuse the non native speakers, an American "biscuit" is a baked good sort of like a savory scone.
Correct, they are different things. A canteen or cafeteria is like a refectory; somewhere (often basic) provided by a school or place of work for pupils or workers to get food and drink on-site, often at discounted prices. A cafe is a commercial establishment for anybody to visit; less formal and expensive than a restaurant, and generally serving lunch rather than dinner, but otherwise the same idea.
An American biscuit tends to be more round in shape and usually doesn't have a sweet, sugary glaze covering it. I personally prefer to take it while it's hot out of the oven and slice it open in the center and spread some butter and jam and eat it with my breakfast. Others prefer other sweet spreads in the middle like honey or some other sweet spread. It's really a breakfast treat.