하고 , (이)랑

하고 and (이)랑 are almost always interchangable, but (이)랑 is more colloquial and casual, and not often used in formal settings.

• 우유랑 빵

  milk and bread

• 우유하고 빵

  Milk and bread

Depending on the context of the sentence, 하고 and (이)랑 can also mean with. It is usually very easy to whether the meaning is "and" or "with".

• 친구하고 영화 봤어요

  I saw a movie with a friend

To make the meaning of the sentence clearer; add the word 같이 after 하고 or (이)랑.

• 누구랑 같이 갔어요?

  Who did you go with?