How can I create a curve defined by a function or by coordinates?

I want to create a curve starting from a given function.
For example I want to create circle using the function x^2+y^2=1

Or, I want to create a sketch in which a curve goes through a set of coordinates. For example I want to create a NACA airfoil profile given the coordinates present in this website:
http://airfoiltools.com/airfoil/details?airfoil=naca4418-il

Thank you very much for your help.

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