Hi Arjan Gelderblohm,
Here is your file back. I have set everything in the way I think you like to have it.
The first object under the Sweep is the Profile, it defines the contour of the Sweep. Its size matters, but not very much if the Rail-Scale is checked on, in case of a third child.
The second object represents the Path. Which is the path were the Profile will be used along it.
The third spline is an option, not a must have. However the raid stabilizes the result. It is like a guide to orient the profile along the second. It has more options, as in scaling the Profile, if the Use Rail Scale is checked on. Then the distance between the spline (second) and the spline (third) will be used, always along the whole path while the position of the second matches the third in progress.
Scene file:
https://www.amazon.com/clouddrive/share/c3RhPnU882zFv2hi9PhwKIWsAzGhvf3p2cs7H4pt96D
Whenever a parameter is not clear, use the right mouse click on the parameter and call up the help content for this specific option/parameter/tool, etc.
I guess you know that since long, but writing in a forum, I have to mention it, from time to time.
https://help.maxon.net/us/#OSWEEP
I have to check in the morning (Done, see edit) again about Sweep tutorials, I guess I have clicked through ten of the one who had anything to do with Sweep (Nurbs), but somehow, nothing goes really one time through ALL the options.
All the best
Edit:
Tutorial Suggestion
https://www.cineversity.com/vidplaytut/nurbs_-_part_four
.
https://www.cineversity.com/vidplaytut/adjustable_bolt_02
https://www.cineversity.com/vidplaytut/getting_started_with_cinema_4d_part_11
https://www.cineversity.com/vidplaytut/cinema_4d_lite_reference_sweeping_Splines