/ - root directory
Everything in your Linux system is located in the directory /, also known as the root directory. It may seem that the directory / something like C:\ in Windows - strictly speaking, this is not the case, because in Linux there are no letters in the names of the drives. At that time, as other markup would be in D:\ in Windows, this other markup would appear in a different folder in the directory / Linux.
/bin - essential user binaries files
Directory /bin contains the necessary user binaries (programs) that must exist when the system is running in single user mode. Applications such as Firefox, are stored in /usr/bin, and the most important system programs and utilities such as bash-console are stored in /bin. Directory /usr may be stored on another markup - the location of these files in the directory /bin creates confidence that the system will be an important tool, even if not connected to other file systems. Directory /sbin similar to it: it contains the necessary binaries for system administration.
/boot - static files for download
The /boot directory contains the files required to boot the system - for example, files of GRUB and your Linux kernel is stored here. Although there are no configuration files boot the system, they are located in /etc, along with other configuration files.
/cdrom is the mount point for CD-ROM
The directory /cdrom is not part of the above-mentioned standard FHS, but you still can find it in Ubuntu, Linux Mint and other distributions. This is a temporary place for the CD-ROM drive connected to your system. However, the standard location for temporary media devices is a directory /media
/dev - device files
Linux sees the devices as files, and the directory /dev contains special files that represent devices. It's not quite such files as we are accustomed to see them, but they are represented as files - for example, /dev/sda is the first SATA drive in your system. If you want to change it, you need to open the disk editor and edit the /dev/sda.
This directory also contains a pseudo device that represents a virtual device that is not related to the equipment. For example, /dev/random generates a random numbers, and /dev/null is a special device that does not produce output data and automatically removes all input data - when you give the command to produce the output to /dev/null, in practice the output is not performed.
/etc - configuration files
The /etc directory contains configuration files that can be edited manually using a text editor. Note that the directory /etc/ contains important system files, but the configuration files for specific users stored in the /home folder.
/home - user home folders
The /home directory contains the home folders of all users. For example, if your username is bob, then you have a home directory in /home/bob. This folder contains user files and data related to the user preferences files. Each user has write access to only their home directory, and to modify other files in the system need to become the root user or edit permissions for files specifically.
/lib essential shared libraries
The directory /lib contains libraries needed by the binaries that are located in the directories /bin and /sbin. Libraries needed by the binaries folder /usr/bin are in the directory /usr/lib.
/lost+found - recovered files
Each Linux file system has a directory /lost+found. If a system crashes, the next boot will check the file system. All found corrupted files are placed in the directory /lost+found, so you can try to recover as much data as possible.
/media - removable media device
Directory /media contains subdirectories, which are mounted media devices connected to the computer. For example, if you insert the USB drive into your Linux system, in the directory /media will automatically create a folder for it. You can access the contents of the USB going into this directory.
/mnt - temporary mount point
For example, if you mount the partition with Windows to restore files, you can mount it to /mnt/windows. However, you can mount other partitions anywhere.
/opt - optional packages
The /opt directory contains subdirectories for additional packages. It is often used proprietary software that does not comply with the standard file system hierarchy - for example, proprietary software can send your files to /opt/application when you install it.
/proc - kernel files and processes
The directory /proc similar to the directory /dev, because it does not contain any of the standard files. It contains special files that represent the system and process information.
/root - home directory root
Directory /root - home directory for the root user. Instead reside in the /home/root, it is placed in /root. It is necessary to distinguish this directory to /, which is the system root directory.
/run is not changed application files
Directory /run - fairly new, and it provides applications with a standard place to store transient files, such as ID processes and sockets. They cannot be stored in /tmp, because the files in /tmp can be deleted.
/sbin - binary files system administration
Directory /sbin similar to the directory /bin. It contains the necessary binary files that are most likely to use the root user for system administration.
/srv service data
Directory /srv contains data for services provided by the system. If you use Apache HTTP server to work with the web site, the more likely you store your website files in directory /srv.
/tmp - temporary data
Applications store temporary files in /tmp. Typically, these files are deleted when the system restarts, and can be removed at any time by such utilities as tmpwatch.
/usr - user binary files and read-only data
Directory /usr contains applications and files used by the users. For example, are not necessary for operation of the system apps are stored in the directory /ur/bin directory instead of the directory /bin, and not the necessary binaries for system administration are stored in the directory /usr/sbin instead of /sbin. Libraries for each application are stored in the directory /usr/lib. /usr also contains other folders - for example, architecture-independent files, such as graphics, are stored in /usr/share.
In the directory /usr/local are normally installed applications, compiled locally - because of this they do not clog up the rest of the system.
/var - variable data
Directory /var writable analog /usr, where usually the files should be read-only. Log files and everything else that should be written to /usr during normal operation, is recorded in the directory /var. For example, you can find the log files in /var/log.