I learned most of the file system of linux and freebsd by experience. For example, I learned that to modify your display resolution, you modify /etc/X11/xorg.conf. Other config files are usually in an ‘etc’ directory. ‘bin’ directories are binaries, ‘lib’s are libraries, etc.
Then later I found that there’s a man page for this. Try the hier man page to see the documented file system structure of your system.

man hier