Mount command is used for attaching the file directory of a device or partition to the file directory tree of the Linux system.
mount /dev/hdb1 /backup
This command will connect the device "/dev/hdb1" to the directory "/backup" so that one can access the files and folders under the "backup" directory. The directory "backup" is also called the "mount point" which must already exist when this command is executed.
umount /dev/hdb1 /backup
This command is used to unmount the backup directory so one can not access the files and folders under the backup directory.