/ Begins the file system structure, call the root.
/home conatins users' home directories.
/bin Holds all the standard commands and utilities programs.
/usr holds those files and commands used by the system
/usr/bin Hold user-oriented commands and utility programs
/usr/sbin Holds system administration commands.
/usr/lib Holds libraries
/usr/share/doc Holds Linux Documentation
/var/spool Holds spooled files
/sbin Hold system administration commands for booting the system
/varHolds files that var mailbox, data files, program files, etc
/dev Holds file interfaces for devices
/etc Holds system program config files and other system files.
Here is a break down of Files structure it may var from distro to distro.