If you want to learn mold design, you must first understand the steps of mold processing, not necessarily, but you must understand and know which steps a set of mold needs to be processed. Then you must know the mold structure very well, that is, you can assemble it yourself, in other words, you can fitter. Finally, you must be proficient in the requirements of designing software, such as UG, Pro/e, CAD, etc. I wish you success!