The shape of the swept blend is determined by the starting shape, the ending shape, and the 2D path that you specify.
For information about using swept blends in families, see Creating Family Geometry.
Video: Create a Swept Blend
The Swept Blend tool allows you to create a blend that has 2 different profiles and then sweep it along a path. The shape of a swept blend is determined by the 2D path you either sketch or pick and the 2 profiles you either sketch or load.

The following procedure is a general method for creating a swept blend. Steps may vary depending on your design intent.
To create a solid or void swept blend
 Forms panel, do one of the following:
Forms panel, do one of the following:  (Swept Blend).
 (Swept Blend). 
 (Void Swept Blend).
 (Void Swept Blend).  Work Plane panel
Work Plane panel
 (Set).
 (Set). Do one of the following on the Modify | Swept Blend tab Swept Blend panel:
Swept Blend panel: 
 (Sketch Path) to sketch a path for the swept blend.
 (Sketch Path) to sketch a path for the swept blend.  (Pick Path) to pick existing lines and edges for the swept blend.
 (Pick Path) to pick existing lines and edges for the swept blend. To select edges of other solid geometry, such as extrusions or blends, click Pick Path. Or pick existing sketch lines, watching the status bar to know what you are picking. This method of picking automatically locks the sketch lines to the geometry you are picking and allows you to sketch the path in multiple work planes, hence allowing for a 3D path.
 (Finish Edit Mode)
 (Finish Edit Mode) The end point for Profile 1 on the swept blend path is highlighted.

 Swept Blend panel, and select a profile from the Profile drop-down.
Swept Blend panel, and select a profile from the Profile drop-down. If the profile you need is not already loaded in the project, click  (Load Profile) to load the profile.
 (Load Profile) to load the profile. 

Enter values for X and Y to specify the offset for the profile.
Enter a value for Angle to specify the angle of the profile. The angle rotates the profile around the profile origin. You can enter negative values to rotate in the opposite direction.
Click Flip to flip the profile.
 (Edit Profile).
 (Edit Profile).  (Finish Edit Mode).
 (Finish Edit Mode).  Swept Blend panel
Swept Blend panel
 (Select Profile 2).
 (Select Profile 2).  Swept Blend panel, click
Swept Blend panel, click  (Edit Vertices).
 (Edit Vertices).  Vertex Connect panel, select
Vertex Connect panel, select  (Controls on Base) or
 (Controls on Base) or  (Controls on Top).
 (Controls on Top).  (Twist Right) and
 (Twist Right) and  (Twist Left) tools to twist the swept blend.
 (Twist Left) tools to twist the swept blend. 
 (Finish Edit Mode).
 (Finish Edit Mode).  , and specify a material.
, and specify a material.