아/어서
Attach -아/어서 to a verb stem to connect actions in order, often meaning 'and then' or 'so.' In this story, '앉아서' shows that sitting happens before looking at the water. You can reuse this pattern in many simple sentences. For example, 저는 벤치에 앉아서 물을 바라보았어요.
저는 벤치에 앉아서 물을 바라보았어요.
I sat on a bench and looked at the water.
