Mounting makes file systems, files, directories, devices, and special files available for use at a particular location. It is the only way a file system is made accessible.
The mount command instructs the operating system to attach a file system at a specified directory.
You can mount a file or directory if you have access to the file or directory being mounted and write permission for the mount point. Members of the system group can also perform device mounts (in which devices or file systems are mounted over directories) and the mounts described in the /etc/filesystems file. A user operating with root user authority can mount a file system arbitrarily by naming both the device and the directory on the command line. The /etc/filesystems file is used to define mounts to be automatic at system initialization. The mount command is used to mount after system startup.