Fitted Spline
Create a fitted spline to be used either as a building block for constructing geometry or as a wire. The fitted spline fits a smooth curve through all the node points in the definition.
Fitted splines are smooth over the entire path (no sharp corners). Fitted splines are preferred over polylines when reconstructing geometry from points (for example, exported from another source) since they do not cause mesh vertices to be created at the node points.
On the Construct tab, in the Create Curve group, click the Fitted Spline icon.Tip: Press V,3 to use the shortcut key.

Point 1 (P_{1})  The starting point of the curve. 
Point 2 (P_{2})  The second point through which the spline curve will pass.  
...Point n (P_{n})  The additional points through which the spline must pass. There may be an arbitrary number of points. 