This is just a simple trick for helping you keep track of your hard drives easier. Just like you can rename a file or folder by right clicking on it and selecting rename (or pressing F2 after left clicking on it), you can also select a hard drive and rename it so that it is easier to keep track of. If, for example, you have one for backups, one for media files, and a main drive, you could name each one respectively to keep things organized.
This trick also applies to all types of removable media. USB thumb drives, memory cards, and external hard drives can also be named so that when they are connected to any machine, they show up in File Explorer with whatever name you gave them. This makes it easier to determine which device was just connected.