Almost everything you do on a computer involves one or more files stored locally or on a network.
Your filesystems lowest folder root / contains the following folders: (at a bare minimum)
|Essential user-related system binaries (for use by all users).
|Static files of the boot loader, only used at system startup.
|Device files, links to your hardware devices such as: /dev/sound, /dev/input/js0 (joystick), etc. For use by the system when accessing these devices.
|Host-specific system configuration files for various daemons, services or startup applications and routines.
|User home directories. This is where you save your personal files and where your unique configuration information is kept which distinguishes you from other users.
|Essential shared libraries and kernel modules which the system accesses while running programs.
|Mount point for a temporarily mounted filesystem like /mnt/cdrom or a USB stick
|Alternative mount point for a temporarily mounted filesystem like /mnt/cdrom or a USB stick
|Optional location for add-on application software packages that do not normally come with the system.
|/usr is the second major section of the filesystem. /usr is shareable, read-only data. That means that /usr should be shareable between various FHS-compliant hosts and must not be written to. Any information that is host-specific or varies with time is stored elsewhere. Icons, documentation and other similar files are kept here.
|/var contains variable data files. This includes spool directories and files, administrative and logging data, and transient and temporary files. Here is where you’d look for error logs, access logs and various other administrative logs.
|System information stored in memory mirrored as files.
The only folder a normal user needs direct read/write access to is:
/home/user/ – this is where you will be keeping all your personal documents, music, videos, pictures, etc.
Files are case sensitive, “myfile” and “MyFile” are two different files.
For more details, check out: Linux Commands