So say you want to try out several Linux distros before you want to install them. With many distros you can get them installed on a Live disk, a CD that let's you run a sort of safe mode version of the OS before you actually install or overwrite anything.
First you probably want to read up on the various distributions available. You can do that at Distrowatch.
Second, once you find some distros of Linux that appeal to you go to: OSDisc and order either a disk or a thumb drive for each version.
Recently I ordered:
Pear OS - which tries to look like Mac OS X as much as possible.
Mint Linux - which has a user interface most Windows users will find familiar. Mint is packed with stuff right out of the box to be useful for both beginners or power users alike. This is a good choice for first timers.
Kubuntu - this uses the KDE user interface which is intended to be friendly to people moving over from Windows. KDE not only is a GUI over Linux but they have many applications that also use the same GUI architecture throughout. This can be handy for businesses that have employees that seem to learn computer skills by rote memorization.
More on these when I get them in.
Why Linux? Years ago I left Windows Me for OS X because I got tired of being an Unofficial Microsoft beta tester. OS X on a Mac gave me rock solid stability although the price was not having as much software to chose from. Over the years more software became available but Apple became more of a Wallet Garden.
Somewhere along the line I tried Linux and liked it. Linux has all the stability of OS X and no walled garden. Tons of free software too. All operating systems do the same things, any of the desktop Linux flavors are mature enough that the average user never needs to resort to a command line.
If you have an old Windows machine you might want to give a few Linux distros a try.