Let's Get Serious
Okay, you've tried out a bunch of live CDs, and now you're ready to install Linux on your PC. Let's assume that you've decided to go with Ubuntu and that you're installing it on a Windows machine (yes, some people do install Linux on a Mac). If you are new to the Linux world and still rely on Windows for certain programs, or if you need to use Windows for your job, you can install Linux alongside Microsoft's OS in a dual-boot configuration. This way, each time you boot up your system, you can choose to run either Windows or Linux.
Ubuntu comes with a handy feature called Wubi (Windows-based UBuntu Installer) that lets you access Ubuntu inside Windows as if it were an application. Like a live CD, Wubi may cause Ubuntu to run a little bit slower than it normally would, but it will give you the chance to acclimate to Linux if you aren't willing to jump in right away.
Once you learn your way around the system, Linux is just as easy to use as Windows or Mac OS. But Linux differs from those systems, and consequently it takes some getting used to. For this reason, you may want to take your Linux transition slow.
The alternative is to adopt what my colleague Tony Bradley calls the scorched-earth option: Wipe out Windows and install your Linux distribution as the sole OS on your machine. This is the method I chose when I moved to Linux full-time, and I found that going this route was fairly easy. The only major drawback of this approach involves needing to run a piece of custom software built on Windows or OS X for your job. If that's your situation, you should probably go with a dual-boot solution.
Creating a dual-boot environment doesn't require much heavy lifting. Many Linux distributions provide step-by-step instructions for installing Linux on a Windows PC in a way that supports peaceful coexistence. Ubuntu offers dual-boot setup directions, as does OpenSUSE. Also, consult PCWorld's "How (and Why) to Partition Your Hard Drive" for advice on how to lay the groundwork for creating a dual-boot PC.
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The Terminal (Mostly Optional)
You can spend your whole computing life inside Linux and rarely have to open a command line prompt to get things done. Nevertheless, learning at least a few basic operations can be helpful, though doing so is entirely optional.
Bash (Bourne again shell) is the standard command line interpreter for most Linux distributions (as well as for Mac OS X), and it's a lot easier to use than you might think. Among the helpful commands that you may wish to learn are how to create empty files and directories (folders), how to search for and kill a running process on your system, how to view hidden directories, how to switch between directories, how to open files and applications, the 'locate' command, the 'find' command, and the 'grep' command. At some point you may also want to learn how to install an application from the command line; but with a system such as Mint or Ubuntu, that method should rarely be necessary.
You can find many novel uses for the command line, too. For instance, you can use Bash to run a text-only Twitter client called TTYtter, learn to use command-line text editors such as Vi or Emacs, try a simple to-do list program called Todo.txt, use Python as a handy calculator, browse the Web with the text-only browser Lynx, run system backups using Rsync, create text shortcuts (called aliases) for executing daily tasks, and automate tedious or repetitive tasks (such as backups) using Cron. All of these operations and programs are much simpler to use than you might think, and learning them will greatly enhance how you use your computer.
Even if you're not interested in the command line, you may need to access the Terminal to deal with occasional (but increasingly rare) hardware problems such as adjusting a laggy mouse driver. Otherwise, you can live happily inside Linux without ever opening the Terminal program.