GNU’s international undergraduate notices typically instruct applicants to apply online (via Study in Korea), upload required documents, and also ship the required documents by the deadline—so you should expect both an online upload set and a mailed set.
Exact document lists vary by program (undergraduate vs. graduate; department; scholarship track), but commonly requested items include: application form, passport/ID, proof of nationality, graduation certificate/diploma, transcripts, and program-specific forms like study plan/personal statement and recommendation letters (especially for scholarships).
Recipient experiences show how document-heavy scholarship routes can be: Nabila Azzahra wrote that she “made detailed checklists” and “started preparing documents several months before the official announcement,” and Almala Nur Fitriana warned that preparing documents took time because “many needed to be apostilled.”