To create a NURBS model, use one of the methods described here.
To create a top-level, parent NURBS object:
- Add a NURBS curve from the Shape panel of the Create panel.
- Add a NURBS surface from the Geometry panel of the Create panel. When you use this technique, the NURBS surface is initially a flat rectangle. You can alter it using the Modify panel.
- Convert a standard geometry primitive to a NURBS object.
- Convert a torus knot to a NURBS object.
- Convert a prism extended primitive to a NURBS object.
- Convert a spline object (Bezier spline) to a NURBS object.
- Convert a patch grid object (Bezier patch) to a NURBS object.
- Convert a loft object to a NURBS object.
To convert objects to NURBS format, use the Modify panel: Right-click the object's name in the stack display (see Modifier Stack) and choose Convert To: NURBS.
In viewports, the quad menu also lets you convert objects to NURBS. Select and then right-click the object, and in the Transform (lower-right) quadrant, choose Convert To: 
Convert to NURBS.