/ : root of the file system contains all devices and directory’s
/root : the root users home directory
/home : all other users home dirs reside in here
/boot : All the kernels and boot specific info
/tmp : temporary files are stored here, is commonly world writable so keep an eye on it
/dev : on linux even hardware devices are part of the file system, they are stored here.
/bin : executables that should be safe for normal users to run
/var : the system writes data here during its operation, commonly contains/var/lib/mysql and /var/www
/opt : optional software, 3rd parties stick stuff here
/sbin : system executables that only root should need
/proc : the OS uses this to keep track of everything on the system in real time. No need to muck around in here
/mnt or /media: this ware new file systems get mounted (cds, floppys, flash drives)
/etc : all config files