I'm going to go in alphabetical (alpha beta cal) order. We are starting with the arch folder.
arch FOLDER
This seems to have the information for different SoCs, for example, ARM and x86.
THE block FOLDER
I have no idea.
THE Documentation FOLDER
Literally documentation for the Linux kernel.
THE LICENSES FOLDER
All the different very boring licenses that are used in the Linux kernel.
THE certs FOLDER
Best guess judging from files (blacklist.c, blacklist.h, system_certificates.S), it's for blacklisting people and making sure everything is secure.
THE drivers FOLDER
This has alllll the device drivers, and when uploading to my OS's Google Drive folder, it took overnight there were so many dang files!
THE fs FOLDER
This has the information for different filesystems, e.g, the Unix filesystem and the FAT filesystem.