In modeling curved surfaces, the line is the fundamental object. Following is a beginner's guide to manipulating lines, and an introduction about how they are used in modeling curved surfaces.

To start a line, one may select an open line or closed line from the tool palette.
One can also right click on any figure window and choose from the pop-up context sensitive menu.
Start the line by clicking on the spot where you want the line to begin, then click wherever you want a control point along the line. The control points allow you to easily edit and shape the line.
When the line is complete, double-click or hit Enter to end it. Each of the blue dots are control points.
Upon ending the line, you will see the completed line in white.
To edit the line, you will need to select Modify.
Upon entering modify mode, the control points become visible.
To select a control point, click on it with the cursor or select by pulling a box around it.
Once a control point has been selected you can modify it by using Iron, Smooth or Unsmooth.
Iron moves the control point to form a curve between the two adjacent control points. The pink handles can be pulled to change the contour of the curve in any way you want.
Smooth leaves the control point in place, and again provides handles for reshaping the line. Unsmooth turns the curve into an angle.
There is no need to precisely place the control points when drawing the line. They can be selected later and dragged wherever you want them. Pretty much anything in Shade can be easily edited and changed at any time.
By grabbing the handle and pulling or moving it, curves are easily controlled.
Multiple points can be selected by holding down the Shift key.
With the Shift key held down and four points selected, it was only necessary to use the Iron command once to create this bell curve.
Hitting the Enter key returns it to a regular line. From here on, we will learn methods of using lines for modeling. First we will do Revolve. Choose Revolve from the menu.
Drag the cursor along the axis about which you want the line to revolve and let up off the mouse when you are ready.
The line is revolved into a finished object. It can be left as such or further edited. It can be combined with other objects within a part. We will look at the power of Parts in a later tutorial.
A rendered view of the object we just created.
Lines can also be extruded. Select Extrude from the menu.
Select the line and drag it as far as you wish.
This is a view of the extruded line.
Highly complex curved surfaces can be created by using the connection function. You can copy the line easily while rotating it using the Copy->Rotate command.
We are looking down at four lines we have copied and dragged into place. To drag a line, select it and use the Move->Translate command. Select all four lines in the Browser.
With all four lines selected Modify->Connection will join them into a curved surface.
Viewed from the top, the four lines now are joined together. As with everything in Shade, the object is very easy to edit.
The above object rendered.
©2013 Larry N.Bolch