In Korean, particles go after subject and object unlike in English.

We could classify them into several groups

They are Subject Particle, Object Particle, Possessive Particle, Side by Side Particle, Place Particle and Toward Particle. I name them by the way we use each.

Subject Particle: 는 (neun), 은 (eun). 이 (yi), 가 (ga)

If subject has bottom consonant 은 (eun) or 이 (yi) comes after subject.

If subject has no bottom consonant 는 (neun) or 가 (ga) comes after subject.

Example

My Brother is a 16 years old. - 내 동생은 열 여섯살입니다.

(nae-dong-saeng-eun-yul-yu-sut-sal-im-ni-da)

My girlfriend is attending Seoul University. - 내 여자 친구는 서울대학에 다닙니다

(nae-yu-ja-chin-goo-neun-Seoul-dae-hak-eh-da-nim-ni-da)

My cousin visited us from Korea. - 내 사촌이 한국에서 우리를 방문했습니다.

(nae-sa-chon-yi-woo-li-leul-bang-moon-haet-seum-ni-da)

My friend sent me a letter. - 내 친구가 편지를 보냈습니다

(nae-chin-goo-ga-pyun-ji-leul-bo-naet-seum-ni-da)

*** There is honorific particle.

If subject is an elder like mother, father, teacher, grandparents...

You should use 께서는 (gge-su-neun) or 께서 (gge-su) instead of 는(neun) or 은(eun).

Example

My mother told me to pick up garbage.-나의 어머니께서는 쓰레기를 주으라고 말씀하셨습니다 (na-eui-uh-mu-ni-gge-su-neun-sseu-le-gi-leul-joo-eu-la-go-mal-sseum-ha-shut-sem-ni-da)

Our teacher gave us homework. - 선생님께서 숙제를 내주셨습니다

(sun-saeng-nim-gge-su-sook-je-leul-nae-joo-shut-seum-ni-da)