If you specify a mount point that is also an active directory in the main file structure, the contents of the directory will be hidden while the foreign file system is mounted. When the foreign file system is unmounted, the normal directory contents will appear again. It's usually most convenient to use an empty directory for the mount point. The basic structure of the mount command is mount -t type device directory. Here, type indicates the type of file system to be expected from the new device.
Device describes the device to be mounted and directory is the mount point itself.
You can use a common mount point if you have more than one device to be mounted, however, if you wish to mount several devices simultaneously, they'll each need their own mount point. To unmount a foreign file system, use the umount command. File systems that have open files or applications cannot be unmounted until all files and applications from the foreign file system are closed. Only the root user can mount and unmount foreign file systems. It is possible to set the system to mount foreign file systems automatically on bootup.