Many people who have never seen Linux have the preconception that it is a DOS-like environment where you're expected to use only the command line, and there's no pointing or clicking, and certainly no Mac-esque dock. This actually couldn't be further from the truth! On the contrary, Linux has a staggering number of graphical desktops available, ranging from lightweight window managers like Fluxbox or Enlightenment to full-blown desktops like Gnome, KDE and XFCE. In fact, there's so many that it can be extremely confusing to a newbie. "Which one should I use?" is a common refrain.
In truth, I can't give a good answer to that, because we're all different and have different needs. You may prefer one desktop over another, or you may need to use something lighter because your machine isn't fast enough to run a full desktop. What I can do is give you some idea of what to expect from each, and what to bear in mind when choosing a desktop. Don't worry though, you can easily change your desktop without having to install a new version of Linux.
Although they are far from being the only ones available, I don't think anyone will disagree when I say Gnome and KDE are far and away the most popular desktops within Linux. These two are the most widely used and most advanced desktops available within Linux, and the chances are you will wind up using one or the other.
If you're using Ubuntu, then Gnome is the desktop that is installed by default:
It's a little like the Mac desktop in some ways. Don't be put off by the colour! A lot of people do seem to dislike the colour choice for Ubuntu, but you can change that easily once it's installed - you have several alternative wallpapers and themes available.
Gnome is a good desktop - it's reasonably fast, and has good applications. It's the default desktop for Ubuntu, and is simple enough that it's easy to use, yet also powerful enough for most things you could want. It's a bit of an adjustment from Windows, however.
If you like the layout of Windows or you consider yourself a power user, then KDE may be a better choice. It's laid out in a similar fashion to Windows, so you may find it easier to get used to. Also, it's got some very powerful features which Gnome can't match.
This is the KDE desktop in Kubuntu. Like in Windows, by default there's a bar at the bottom, with the main menu at the bottom left.
I'm unashamedly a KDE man myself - it has a lot of features I like. It has an excellent application launcher called Katapult - just press Alt+Space and it will appear, then start typing the name of an application and it will find it for you. Then press Enter and it will launch it. Konqueror is also a great asset - it's an extremely powerful file manager which doubles as a web browser, and has integration with many other KDE applications. However, if you just want to open files, KDE now has a lightweight file manager called Dolphin which is the default file manager.
Finally, there's XFCE. It's more lightweight than either Gnome or KDE - think of it as a quicker, faster version of Gnome. It's a good choice for older machines which don't have the processing power to run Gnome or KDE at an acceptable speed, or if you just want a really fast desktop.
You can still use all the same applications in XFCE as you could in Gnome or KDE, but you will notice a significant difference in speed.
Ultimately, the best advice I can give is to try them all out to see which you like the best. Although applications are usually designed with one of the desktops in mind, most Linux applications will work on all of them. I'll give details of how to install a new desktop in a future post.