"bare" and "kun" are almost interchangeable. "bare" is more common than "kun" though. "Det er bare/kun to igjen" = "There are only two (items) left" "Det koster bare/kun 100 kroner" = "The price is only 100 kroner" "kun" emphasizes and therefore it is often used in commercials. "bare" is very versatile and is often used to de-emphasize. "kun" means only "only", "bare" can both mean "only" and "just". "Jeg gikk kun til butikken" = "I only went to the shop" (and nowhere else) "Jeg gikk bare til butikken" or "Jeg bare gikk til butikken" = "I only went to the shop" or "I just went to the shop" If you wonder which one to use, "bare" will be most correct in most cases. You can actually speak perfectly Norwegian without using "kun". :)

There are also some expressions with "bare". Most common is "det er ikke bare bare" which means that something is not very easy or that something is quite difficult to do.