How it works
If all that came in a brand of Linux was Linux, you wouldn’t like it for your desktop. Linux is similar to DOS in that it’s natural interface is a black screen with white text and you have to type in everything you want to do. Luckily, some people got together and built XWindows. XWindows is a layer on top of Linux that lets you have a desktop with a mouse pointer etc. But XWindows isn’t very pretty. To have a good looking desktop, you need… a desktop.
When you install most brands of Linux, you can choose a “desktop.” The two that are included in most brands of Linux are the Gnome Desktop and the KDE. A “desktop” in this sense is just the layer you see. Linux is essentially the same, but each of these desktops provide a framework for programs to run in. For example, think of all the little windows that pop up to tell you something, like an error. Linux is telling you there’s an error, but it does this through the little window that the desktop provides. Think of it as a mask that Linux and XWindows wear to improve the way they look. You can wear either mask. The principal difference is in how they look. But there are also many programs made for each desktop that need that specific desktop to run.
Which is better?
Ah, the eternal question. This is sometimes a divisive and bitter question. Most recently, some have said that Gnome and KDE should merge, and not just because it would solve a lot of arguments. The interesting thing is that since they are both just a framework of files the computer needs, you can actually choose to install both. After installing both, when you log in, you can look for a “Session” menu and there select which one, Gnome or KDE, you want to use this time. Also, if you install both, but choose to run Gnome, for example, the computer still has the files it needs to run KDE, so it is still able to run KDE programs- even in Gnome!