What is the difference between 얼마 and 얼마나?
Does 얼마나 mean 'How much...?' or is it just used with adverbs or adjectives?

Question

Answer

얼마  how much (money)
얼마예요? How much is it?

얼마나 how + adjective/adverb 
얼마나 커요? How big is it?
얼마나 자주 와요? How often do you come?

Answer

More examples for the word 얼마(-나)

How big is it/that?
(그것이) 얼마나 커요?

How big was that fish (you caugh yesterdayt)?
(어제 당신이 잡은) 그 물고기가 얼마나 (많이) 컸어요?
그 물고기가 얼마 만큼(-이나) 컸어요?