Connection

와, 과, 하고, (이)랑: four ways to say "and"

Korean gives you four particles for joining two nouns. They mean the same thing. The choice is register, plus one spelling rule.

Which one to use

과 / 와 is the formal pair, and it's the only one with a 받침 rule:

• 과 after a consonant: 책과 (chaek-gwa), "and a book"
• 와 after a vowel: 사과와 (sagwa-wa), "and an apple"

하고 is the everyday one. No spelling rule, works after anything, fine in speech and in most writing.

• 책하고 (chaek-hago)

(이)랑 is the casual one, for friends:

• 이랑 after a consonant: 책이랑 (chaeg-irang)
• 랑 after a vowel: 사과랑 (sagwa-rang)

Same sentence, three registers:

• 커피와 빵을 샀어요. — formal, written
• 커피하고 빵을 샀어요. — neutral, spoken or written
• 커피랑 빵을 샀어요. — casual

All three mean "I bought coffee and bread."

They also mean "with"

This is the part that surprises people. The same particles do double duty as "with", and the verb tells you which reading applies.

• 친구하고 갔어요. (chingu-hago gasseoyo) — "I went with a friend."
• 친구하고 저는 학생이에요. (chingu-hago jeoneun haksaeng-ieyo) — "My friend and I are students."

Joining two nouns in a list gives you "and". Attaching to a person before an action verb gives you "with". You'll often see 같이 (gachi, "together") added to make the "with" reading explicit:

• 친구하고 같이 갔어요. (chingu-hago gachi gasseoyo) — "I went together with a friend."

The mistake: 그리고

This is the one worth flagging, because English hides the distinction entirely.

그리고 joins sentences. 와/과/하고/랑 join nouns.

• 커피하고 빵을 샀어요. ✓ — "I bought coffee and bread."
• 커피 그리고 빵을 샀어요. ✗

• 밥을 먹었어요. 그리고 커피를 마셨어요. ✓ — "I ate. And then I drank coffee."

If the "and" sits between two things, you need a particle. If it sits between two clauses, you need 그리고. English uses one word for both jobs, so this mistake is close to universal among beginners and it's an easy one to stop making.