The Filesystem of the UNIX family is very well organized. There are a handful of compatible naming conventions used by various systems. For example, /etc is usually used for critical system and configuration files. /sbin and /bin have the important utilities. /tmp are for temporary files.

Without further ado. Here are the standard directories used by most UNIX systems

Pathname Functionalities and Contents
/bin Operating system commands. In some systems /bin is a symbolic link to /usr/bin
/boot Kernel and files needed to load the kernel
/dev Device entries for disks, printers
/etc Critical system and configuration files
/home Home directories for users
/lib Libraries, shared libraries
/opt Optional software packages
/sbin Commands needed for minimal system operability
/tmp Storage for temporary files
/usr Contains more folders inside
/var System specific data and configuration files

This can serve as a reference in the future for anyone wanting to learn the filesystem of the UNIX family