Autodesk® 3ds Max®: All About "SPLINE" in Computer Graphics

SPLINE might seem like a unconventional way of modeling for some people but in practice they have many uses. Some types of modeling, such as vehicle and aircraft design, require these smooth curves to define the shape of the object.
Spline has a long history. Back in the ship building days of yore (early AD), naval architects created their hull designs by bending a strip of wood over and around the series of weights, creating a smooth curve. The piece of wood was called a “Spline”. In computer graphics, this idea was borrowed to create what is now called a spline. Some modelers avoid spline and say they take too long to adjust. But if you learn to draw them right, you will love to model things using them.
I won’t lie saying that the very first time I started using spline, I think it is just unnecessary thing in 3ds max but gradually I figured out some key things in them and came to know that it is the second most powerful technique to model things in 3ds max.
The factors that determine the shape of the spline are the placement of the vertices and the curves going in and out of them. You can get a large curve out of just two well-placed vertices. The fewer you use, the easier it will be to adjust the curves.

Start by drawing as few vertices as possible and see what you can get out of that. When drawing a spline, a single click makes a corner vertex, where the spline will go straight in and out of the vertex. To get a little curve on it, click and drag the mouse while placing the vertex.
The two key points to get into your head are: You do not have to drag all the way to the next vertex before releasing the mouse button. Once the curve looks good for all the vertices drawn so far, release the mouse and move it to the next spot. You don’t even have to drag in the direction of the next vertex. Learn to ignore the line between the last vertex and the current cursor position, as this does not determine the shape of the line. After you drag to make the curve shape, you can release and move the cursor and place the next vertex anywhere you want. It is better to use the “corner+Smooth” creation method.

After you have drawn your nearly perfect spline, you can move vertices around and adjust their handles if they are the Bezier type (if they are not you can anytime choose “Bezier Type” from quad menu by right clicking for the selected vertex.)
It takes practice to get good at drawing splines, but really no more than an hour or two. That’s all it takes to find the secrets of spline. Just feel how good you will feel when you can create them quickly with no muss and fuss.