Since he has some experience already with CAD, the learning curve shouldn’t be too high. It took me about a week of playing around to start to get comfortable with it. I do have a lot of prior 3D CAD experience, however. Before Fusion, I had been drawing in Solidworks, Creo, AutoCAD, and Rhino since about 2011.
For a crash course in the user interface, Lars Christensen does a good job in this video:
I found these YouTube tutorials very helpful when I was first learning Fusion. They help cover building assemblies from sketches, user variables, nesting parts, and setting up CAM toolpaths.
I made the flat pack stool from the second video here.