Using a bar of bath soap is not a good substitute for a real shave soap, as you have found out. Yes, it can be done but it is a desperation move when you have nothing else and it does not make for a pleasant shave. Two different products meant and formulated for two different purposes.
The DE Vergulde Hand shave you picked up should be very good shave soap if it is anything like the Ver Guldehand shave stick soap I have. It should do the job nicely.
Here is a vid on how to make a lather with shave soap. I have found his series of vids very helpful.
https://www.youtube.com/watch?v=_4zESTQWDuw
Try practice lathering without shaving to get the hang of it. Good luck.
Bob