From MSDN GraphicsPath.AddCurve:
The curve begins at the point in the array specified by the offset parameter and includes the number of points (segments) specified by numberOfSegments.
http://msdn.microsoft.com/es-es/library/ms142523(v=vs.110).aspx
So if you use the overload without offset, you can asume offset is 0, so it will begin to draw at p[0]
If what you tried to mean is that you want to set a drawing offset (displace the coordinate system 0,0) then you can apply a transform with Graphics.TranslateTransform.