In Korean, we use special little words called particles to tell us more about where something happens or where something is. Two important particles for talking about location are 에서 (eseo) and 에 (e). They help us understand if something is happening at a place or if something is just located at a place.
Let's imagine you are playing at the park. You would say, 'I play at the park.' In Korean, you would use 에서 because playing is something you do there. Now, if you are just saying where the park is, you would use 에 because it's just about the park's location.