This grammar pattern is used with a noun to show the target spot or a space of an action. It is used only with a transitive verbs and can be changed with ‘에’.
● 공책에다가 제 이름을 적어 놓았어요. (I wrote my name down into the notebook.)
● 책을 책상 위에다가 놓았어요. (I put the book on the top of the table.)