I use FreeCAD and it's pretty good. But I think it's impossible to learn by trial and error.

MangoJelly has done an amazing job in churning out high quality tutorials for FreeCAD: https://www.youtube.com/watch?v=t_yh_S31R9g&list=PLWuyJLVUNt...

(this is just one playlist, there's a lot more on his channel).