Actually, it depends on what you focus on If you want to look at the drawings or product process more conveniently, you can look at the following: mechanical drawing, tolerance and cooperation, mechanical manufacturing basis, mechanical engineering materials, metal materials and heat treatment, mechanical manufacturing technology and interchangeability, and technical measurement.

In order to understand the working principle of mechanical equipment, learn some mechanical principles, hydraulic transmission, electro-hydraulic proportional technology, servo control system, mechanical engineering control foundation, programmable controller and common control appliances, general mechanical equipment will have plc control and hydraulic system control.

In fact, there are many books here, and it is convenient to buy second-hand books at the university. You are a salesman. You may have to tell your customers how your product works, or you may be asked some jargon. I think this is based on experience and accumulated slowly.