Autodesk Fusion 360 is one of the most powerful tools for 3d printing. I think the best way of learning is through praxis. You can start designing your own shapes with Fusion 360 right from the beginning with the help of the videos and lectures in this course. This course also includes quizzes so you can check your knowledge after every project. After this course you will be able to use Sketches in Fusion 360 and design complex models for any purpose (and also 3d print it).