There are a couple of ways to conjoin nouns and sentences in Korean.

One of the ways you can conjoin nouns is to use 과 or 와.

물과 밥만 필요해요 = I only need water and rice.

(물 = water. 과 = and. 밥 = rice. 만 = only. 필요해요 = need)

In the sentence above, 과 was used because 물 ends in a consonant.

케이크와 커피를 샀어요 = I bought cake and coffee.

(케이크 = cake. 와 = and. 커피 = coffee. 를 = object marking particle. 샀어요 = bought.)

Here, 와 was used as “and” because 켸이크 ends in a vowel.

Another way to conjoin nouns is to use 하고.

남동생하고 여동생이 있어요 = I have a younger brother and a younger sister.

(남동생 = younger brother. 하고 = and. 여동생 = younger sister. 이 = subject marking particle. 있어요 = have)

However, 하고 is used in informal situations. Unlike 과 and 와 it doesn’t matter as to whether 하고 follows a consonant or a vowel.

To conjoin sentences, use 그리고.

동수는 미국에 살았어요. 그리고 동수 여자 친구도 미국에 살았어요.

Dong Su lived in the U.S. and Dong Su’s girlfriend lived in the U.S. as well.

(동수 = Dong Su. 는 = topic marking particle. 미국 = U.S. 에 = locative particle. 살았어요 = lived.

그리고 = and.  동수 = Dong Su. 여자 친구 = girlfriend. 도 = as well. 미국 = U.S. 에 = locative particle. 살았어요 = lived)

그리고 can only be used to put sentences together, not nouns.