The Desktop Environment
Your desktop environment is your system's user interface. It determines how windows and icons are styled and how you navigate through your system. Among the many different desktops available in the Linux world are Gnome, KDE, Xfce, and LXDE. Ubuntu maker Canonical released a new desktop interface in April 2011 called Unity, which is based on Gnome.
The desktop contains various components, but at this point it's enough to know that you are free to choose pretty much whichever desktop environment you want to use. Distributions such as Ubuntu, Mint, and OpenSUSE provide an array of different desktops that you can easily install. Ubuntu 11.10, for example, offers Unity, but you can easily install variants of Gnome. Another alternative is to use KDE in Ubuntu--either by downloading Kubuntu (a variation on the Ubuntu system that installs KDE as your default desktop) or by installing KDE in the standard version of Ubuntu.
The best choice for beginners is to stay with the default desktop environment for your distribution. But desktops in Linux are interchangeable; so as you become more comfortable using Linux, you can try out different desktops to see which one you like best.
The kernel--the software layer that acts as the go-between for your applications and your PC hardware--is the core of any Linux system. This is the component that you are least likely to have to deal with as part of maintaining your system, especially if you choose a beginner-friendly system such as Ubuntu or Mint. But as you delve into the Linux world, you'll probably find people talking about the kernel on forums and help sites, so it's helpful to know what the term refers to.
The stable version of the kernel at this writing is version 3.2.2. If you choose, you can update your kernel as new versions come out, but it's much simpler to wait for your particular distribution to roll out kernel updates.
Time to Try Linux
Now that you have a sense of how some of the Linux distributions differ, it's time to try out a few and see what you think. Unlike with Windows, you don't have to buy a CD or purchase an access code; instead, you can just hop online and download any distro you want to try, for free. And if you don't have the bandwidth to download Linux, many distros will send you an installation CD by mail (usually for a nominal fee).
Many distros--including Debian, Fedora, OpenSUSE, Linux Mint, and Ubuntu--also offer downloadable live CDs. Live CDs let you run the operating system without installing it on your hard drive. That way you can get a better sense of what it will be like to use a particular distro. Live CDs tend to be less responsive (and to run slower) than the actual operating system. The main thing to focus on with live CDs is the look and feel of the interface and the way the system is organized.
To create a live CD you must download the OS and then create a disc image on a blank CD, external hard drive, or USB flash drive. If you've never copied or burned a bootable disc image, try Ubuntu first before moving on to other distros. Canonical has a convenient step-by-step online guide for downloading and creating an Ubuntu live CD using Windows or OS X.