This is a good question Izala. You should ask before you enroll in the class whether you will get to keep the intellectual property (IP), otherwise known as what you create. Here are more resources if you're interested in learning more about IP... http://www.aipla.org/about/iplaw/Pages/default.aspx
That's great that you are interested in studying fashion! What type of class are you looking take? Are you able to reach out to the professor or teacher? I would consider talking to the instructor of the course in order to see what his or her protocol is for designs made while enrolled. He or she may be able to give you more information about the assignments as well as the course overall. Do you know any students who have taken the class in the past? Things change from class to class, so what applied to them may not necessarily apply to you, but it could be worth reaching out to other students in order to get more information, as well!
I hope this helps! Wishing you all the best in your endeavors!
Have a great day!