How do I update a hard drive to the changes I've made on another one?

I know I sound fairly computer illiterate asking this, but I’m pretty sure I’m asking how to synchronize drives. Basically I have my music collection on two hard drives, one serving as a backup. I frequently add and delete stuff from the primary hard drive. How do I update the other hard drive to have all the same changes without manually adding and deleting on the backup as well?

I did notice if I go to the properties of the drive, and click on the “tools” tab, then “backup”, that probably accomplishes what I’m looking for. But is that the best/easiest way to do what I’m trying to do? I don’t want it to rewrite the whole drive, just add and remove stuff, leaving the bulk of the data alone. Maybe it doesn’t matter. I don’t know. I need a geek.