Why -에서 instead of -에?
It is 에서 because 웃다 is an action verb.
You might be thinking its 에 since 방 is a location. It is a location BUT 웃다 determines the marker. There is an action verb being done which is 웃다. So 에서 has to be used.
Here, -에서 denotes where an action takes place.
I cannot learn Korea
why 저는 not 내가?
옷 this looks cute