Want to start small business in Germany while being a student

Little about me: I am a masters student here in Germany and I have some experience in Vintage clothing I have a good supplier based in Pakistan who can send me vintage clothes and I want to sell it on Vinted, ebay etc.

How to proceed further with this? How can I register my small business while doing part time job as well as its not a very profitable business on low scale. Want your idea how to proceed further

Thank you