Your question is not unambiguous.
Are you asking about "best fit" curve fitting or about defining a known type of curve to some points?
Start out by plotting the points on graph paper. See if the plot suggests what kind of curve to fit.
If you know or can guess what kind of curve, then the curve will have parameters which you need to find.
For example, if the curve looks like a circle, it has 3 parameters: the co-ordinates of the center and the radius.
If you have 3 points, then you will get 3 simultaneous equations in the 3 parameters
If you have multiple points to fit to a circle, you are stuck doing least squares curve fitting.
If you can tell me exactly what your question is, I can probably be more helpful.
