Follow shape

In this case, TopSolid'Cam projects the drive curve, following the z-axis and onto the part’s faces. The tool is positioned against the faces and follows the drive curve projection, taking the offset into account.

Follow curve

If this checkbox is ticked, the tool path corresponds to the drive curve, taking into account the tool position, relative to the curve (on the left, on top or on the right).

Follow added faces

In this case, TopSolid'Cam does NOT project the drive curve along the Z axis on the part BUT ONLY on the faces defined in the additional faces. The tool is positioned against these same  faces and follows the drive curve projection, taking the offset into account.