When you are creating a Web site, you will find yourself creating pages, and adding to those pages other elements such as graphics. Naming these files and linking to them is one of the things that can solve problems for you, or create them.
Case is an example.
One of the reasons why this matters is that the Internet is made up of a large number of different machines, with different operating systems, that handle names in different ways. These two platforms do very different things with the case of file names. NT doesn't particularly care. In the Unix world, these are three different files, and you could have all three in the same directory, coexisting peacefully. But in fact you are going to be working with a Unix server here at the College, and you will definitely need to be concerned.