To Create a Spline
1. On the Sketch tab, click 
Spline. The location of the start point is displayed, relative to the base point.
Spline. The location of the start point is displayed, relative to the base point.2. Select a start point.
3. To lock the one of the dimensions of the entity you are creating, press Enter. Press Tab to switch to the other dimensions.
4. Continue selecting more points as needed.
5. Middle-click to exit the tool.
6. To modify the spline shape, click a point and drag it to a new location.