So I am having difficulties to put a heat sink on a PCB, I was not able to find a valid tutorial on Youtube, so can anyone from here tell me step by step how to put a 3D model of heat sink on a PCB board for MOSFET transistor?
There is a great variety of heatsinks, MOSFET packages, dissipated power, moounting methods...
It may be a small one glued on top of the MOSFET, some are soldered besides the MOSFET, some are screw mounted.
Are you trying to put an actual heatsink on an actual board, or are your trying to create a 3D model of a heatsink to place on a PCB in some undefined software that you're not telling us about and would like us to guess what that software is?
You might be able to get a complete footprint/STEP model from the heat sink vendor. If not, you’ll have to create your own. Create the footprint in Altium. Create the model in your CAD program, and generate the STEP model. Import the STEP model into the footprint.