dd is a very dangerous tool because a single mistype of a disk letter will overwrite the wrong disk and cause even more data to be lost. So I would not recommend it for newbies.

For example, you have an empty hard disk at /dev/sdc, your bad hard disk as at /dev/sdb and your operating system is at /dev/sea, normally you'd type dd if=/dev/sdb of=/dev/sdc bs=4K, but if you are careless and are just pressing up and down arrow keys on the terminal to get this command you ran before, you might forget to change "sda" to "sdc" and it will overwrite your OS drive!