It depends on your route (direct application vs. uni-assist) and programme level, but the university’s international-qualification guidance includes common core items such as: a passport identity-page copy, a chronological CV, certified copies of your university entrance qualification and academic transcripts/certificates (with certified translations into German or English if required), plus a certified copy of the required language certificate (German where applicable). For master’s programmes, additional evidence may be required depending on the programme (e.g., specific skills/criteria).
From the recipient stories, you can also see what this looks like in real life: Christine Kigaga described gathering “academic transcripts and certificates” and taking IELTS; Hamza Ijaz focused on TOEFL proof and a coherent motivation/story; and Aruba Irfan stressed the motivation letter as the part where “your story, goals, and passion come to life.”