Help with b-splines approximation on a closed data set

Hello,

I am a post-graduate student and I am new at geometry computing etc. I have an assignment and I have to create a b-spline to approximate a closed data set. I have to make a program that I have to make clicks around a round area on a medical image, and a closed curve using b-spline must be created, showing the points I have clicked, control points that were calculated by the algorithm and the b-spline curve.

Can someone help me with the spline part because I am lost in literature about these topics?

Thank you a lot