Without further context, the most likely translation is: 그냥 숨을 쉬어 (informally). *그냥(just) 숨(breath) 을(object particle) 쉬어(breathe) Depending on the context, there may be several variations. 내쉬다(breathe out), 들이쉬다(breathe in), 쉬어 봐(try breathing), etc.