do need to know how to calculate the points or how to display them?
If you need to display simply use
draw_polyline(points, color, thickness, antialias_bool)where
point is a PoolVector2Arrray(or vector3), and remember that the more point you calculate the smoother it will look like.
If you need to calculate those point you can search on the internet, it´s full of example (i actually found one for C++ in the Italian wikipedia: https://it.wikipedia.org/wiki/Curva_di_B%C3%A9zier#Applicazioni_nella_computer_grafica )