You can't really create 3-D in Flash. Flash is decidedly a 2-D program. But, not to be deterred, Flash users have created many tricks to make you think you're seeing 3-D.

One simple approach is to rotate a 2-D object in what appears to be 3-D space. For example, you can draw a circle and scale it in one dimension so that it becomes progressively more of an oval until all you see is a straight line. Continue to expand it from the line through fatter and fatter ovals until you have a circle again. You've just apparently rotated the circle 180 degrees. Continue until you're finished. You can select a group of frames and copy them or reverse them.

You can use shape tweening to create this 3-D effect. You can shape tween a circle into a line and back again to make it look like it's rotating.

For fancier results, you can use software packages, such as Swift 3D, that are designed for creating 3-D animation for Flash. Also, some high-end 3-D animation packages, such as Maya, have Flash export capabilities built in.