What is the difference between a server and a hard drive?

I know that this is probably a very silly question, but I am new to web developing, and I'm starting to realize that a good way to understand about technology in general is to differentiate seemingly similar ideas. In order to broaden my understanding of technology and its inner workings--could someone to explain to me the difference between a external server, and, shall we say, an external hard drive.

The way I understand it is that a server is exactly the same as a hard drive, only it can be accessed remotely. Can someone confirm this? (or call me stupid and explain the real difference haha)

Also, should I buy a server and use it for some file storage?