The transistor in various flavors are the most complex single devices man has ever created, and likely will ever create, thus requiring an enormous amount of time and effort to understand at the rudimentary level much less master as a Pro.
If one wishes to become a "Pro" with understanding Transistors, then consider taking undergrad courses at a university. These should include fundamental Semiconductor Theory and basic Electronic Circuits wrt the transistor (BJT, JFET, MOS). Once these courses are mastered, then move onto graduate school and take Advanced Semiconductor Theory with Active Device emphasis, and/or Advanced Transistor Devices/Circuitry Theory and Practice which should include detailed analysis and design of active devices like BJT, MOS, JFET, IGBT and so on. Then you can study the various Semiconductor Technologies such as Ge, Si, SiGe, GaAs, SiC, InP, GaN and how they are utilized with the various active device types mentioned, as well as supporting circuitry for these drives types and semiconductor technologies.
This gives one a more detailed overall "look" into how these active devices operate and behave, then you begin to realized the inherent complexity of such and how these devices are actually fabricated for use. Realizing you have just scratched the surface and the True Learning Experience begins, you can truly appreciate the enormous efforts by others in this field.
At this point one realizes the entire process starts all over again with Integrated Circuits, and another career long learning curve which is never ending is awaiting!
Best,