In ordered modeling:

Constructs a protrusion by fitting through a series of cross sections. You can define the cross sections using profiles drawn within the command, sketches, or edges of existing features. The cross sections must be closed elements.

In synchronous modeling:

Constructs a protrusion by fitting through a series of cross sections. You can define the cross sections using sketches, or edges of existing features. The cross sections must be closed elements.

You can also define guide curves (A) (B) to control the shape of the feature. When using guide curves, the planes of all the cross sections must intersect all guide curves.