Computers can store data temporarily in main memory. Many times computers need to store data for long periods of time. Hard drives and disk drives are used for that purpose.
Hard drives reside inside the computer's case. They look something like a can of sardines. Inside the hard drive's case there are several metal disks. These disks are magnetized to hold data. The amount of data that a hard drive can hold is measured in bytes, megabytes (millions of bytes), and gigabytes (billions of bytes). Most modern computers have at least 500 megabytes of hard drive space.
There are many types of disk drives. The most common are called floppy drives. They hold common floppy disks. The problem with floppy disks is that they're very unreliable, and don't hold much information. A typical floppy disk only holds 1.44 Megabytes of data. There are other devices that can hold several gigabytes of data. These devices are generally used to back up data and to carry large files.
Tape drives use magnetic tape to store data. There are several different types of tapes. Older types of tape come in large reels. More modern types of tape come in 8mm cassettes like the ones you would use in a camcorder.