One of the things that makes Linux special is that it can play nice with other operating systems. You can run Linux alongside of other operating systems quite easily. The most popular installation process for installing Linux is to install a Fresh Installation of Linux with no other operating system in place. This allows the computer to dedicated 100% of its resources to running Linux. However, it is quite easy to install Linux as a one of a series of operating systems that a computer has available to it.
Here are the most popular ways to install/run Linux on your computer
Dual Booting - If you want to keep an existing operating system, and install Linux as well, you will have what is known as a "dual-boot" system. That means that you have a PC that can use two different operating systems, and during the boot process you will need to decide which one you would like to boot into.
Author's Note: Dual Booting between Windows and Linux is becoming somewhat less popular due to the rise of Virtual Machines. If you like the idea of running two operating systems, then you may want to consider running Linux as a VM inside of another operating system instead.
Live CD/DVD Booting Linux
If you are just looking to try Linux out to see if you like it, but don't want to commit to wiping out your main operating system, you may want to consider trying Linux from a \"Live CD/DVD\". Many Linux installations provide the option of downloading and running Linux as a \"Live CD\", which means that Linux runs as a completely bootable operating system from the CD/DVD. The files are loaded into your computer's memory, rather than being run for a hard disk drive. In layman's terms, this means that you can run Linux from a CD/DVD, and then when you reboot your PC, and remove the CD/DVD, it will boot back into its old operating system without any difference to your PC. This gives you an easy way to try out several distributions of Linux until you find the one that you like!
Using a "Live CD/DVD" is also a popular method of rescuing files from a corrupted operating system, more on this later...
Linux as a VM inside another Operating System
If you like your current (non-linux) desktop operating system, but would like an easy way to access a Linux desktop or run your favorite open source software, you may want to consider running Linux as a VM inside another operating system. There are a number of ways to do this, but one simple one would be to download and install a Virtual Server application, and then install your Linux distribution under that host software. This topic is covered in the more advanced tutorials on this website I think that I should pause here and say that everything that you can do with your other operating system, you can do with Linux. That means word processing, databases, spreadsheets, Internet browsers, e-mail, photo touch-ups, MP3, CD Players, cameras and then there are a lot of things that Linux has to offer on top of all that that other operating systems don't.
Fresh Install of Linux
This method is by far the most popular installation method available. In this approach, you take the plunge and format your computer's hard drive and install Linux from a CD/DVD. Linux then runs as your computers only operating system.