What are the basic knowledge of plastic injection molding process?

I have to manage a factory because of my new job which engaged in plastic injection molding and whose products are plastic parts. Our materials are mainly PP, TPE, and nylon. I didn't study materials science or injection molding process before, so I hope to understand some basic knowledge of plastic injection molding process. For example: What are the characteristics of different materials during injection molding, and what needs to be paid attention to to ensure molding? What are the common requirements and knowledge of injection molding process? What are the common defective plastic parts and how to improve them?