Questions & Answers about jumare sachoni uri jibe waseo jokarang gati jjigeun sajineul boyeo jwosseo.
주말 means weekend, and 에 is a particle often used with time expressions.
So 주말에 means on the weekend or over the weekend.
Here, 에 marks the time when the action happened. In English we do not always translate it directly, but in Korean it helps show the time setting.
Both are possible in Korean, but they do slightly different jobs.
- 이/가 marks the subject more neutrally.
- 은/는 marks the topic and can add contrast or emphasis.
So 사촌이 simply presents my cousin as the subject of the actions:
- the cousin came
- the cousin showed a photo
If you said 사촌은, it could sound more like as for my cousin... or set up a contrast with someone else.