Autodesk Inventor iDoor Tutorial
Page 25 - Creating the Solid Bodies - The Rails

As soon as you select the point the preview will update to look like the image below. next you need to change the extrude type to Cut by clicking on the button shown...

Select the Point

The preview will change from green to red. now select the Solids button, and click on both rails...

Change To Cut Operation

When selected, the rails will be outlined in a grotesque magenta dashed line. Click OK to cut.

Select The Solids To Cut

The rails are done, and should look like those below...

The Completed Rails