What is the difference between the consonant sound at the beginning of cola, and the one at the beginning of coffee?
Depending on your English accent, I think 커 sounds more like "call", with your jaw open and unrounded. While 코 should sound more like "cocoa", with rounded lips. Correct me if I'm wrong, please.
아 is more like the vowel sound in father, while 어 is more like the sound in awful