File structure (first level) of Linux and derivatives

/ - Root-Directory
/bin - system tools
/boot - kernel, bootmanager
/cdrom - Mount-Point for CD-ROM drives (optional)
/dev - device files
/etc - configuration files
/floppy - Mount-Point for floppy drive(optional)
/home - user directory
/lib - shared Libraries
/mnt - mount Verzeichnis
/opt - additional software, GUI
/proc - system informations
/root - root user directory
/sbin - system programs for root
/tmp - temporary files
/usr - applications for the GUI, source code (kernel)
/var - various files, log files