https://www.youtube.com/watch?v=KyJm9pj_Psg

This ending has many meanings, but I will focus on the meaning that I hit when opening a random page: Express a meaning where one things adds to another.

I found a good explanation on Korean StackExchange that says if 에 means at, 에다가 can be though of as on to. The example in the question was 길에다 토하면 (if you throw up onto the street).

This one is too nuance-y so I am not going to focus on speaking much. No example sentences yet. Worth talking about with a tutor or exchange partner.