BTS (방탄소년단) - 21st Century Girls

Korean Grammar -

V + [서], 서 means 'and', 'then'

저는 학교에 가[서] 공부할 거예요.
I will go to school and [then] study
우리는 집에 와[서] 바로 잤어요.
We came home [and] went to sleep immediately

N + [들], 들 denotes plurality.

우리[들]은 무서웠다.
[We] were scared.
그들은 우리[들]과 놀고 싶어했다.
[They] wanted to play with us.

[건], 건 is shorten for 것은 meaning 'thing'.

이[건] 당신의 책인가요?
Is [this] your book?
네가 뭐라[건] 신경 안 써.
I don't care [whatever] you say.

Let's speak in Korean. -

절대 쫄지 말아.
(jeol-dae jjol-ji mal-a.)
Don't ever be scared.