150-200 page books are a good place to start. man pages are ok for cli tools but for bigger tools and languages, one needs a good book. after gaining some experience, one might want to dive deep into the specification to learn more about the system.
and it takes time. programming skills don't compound if you keep switching context on a weekly/monthly basis. you have to do one thing for years to get good at it. and it takes long sittings at a time. constant context switching isn't helpful, you gain some insights only when you spend some time with the problem.