How does a computer store information on a hard drive?
At the most basic level when a computer writes anything to any media, even going back to the old "floppy" disks, it is in bits and bytes which are simply positive and negative images electronically recorded on the physical media. Some are one time only like a CD, others can be rewritten, some information can only be accessed sequentially, others must have an index.
Hard dirves are made up of bits and bytes, sectors,files, indexes and they all inter-relate to store the information.
The disk drive head writes a magnetic pattern onto the spinning metallic disk similar (but at a much greater speed & density), to the way the old floppy disks worked. A modern disk drive has several individual disks contained in one drive, on the same spindle, and multiple heads between the disks to achieve todays mega and gigabyte capacities, and speed. The head does NOT contact the media, but actually flies above the disk, analogous to a jet flying over a runway at full speed without ever landing. A "touch and go landing" of the drive's head would permanently damage the disk.