A taste of Linux
If you're completely new to Linux and interested in trying it out, I recommend trying out a "live distribution" without installing anything.
You can think of a "distribution" as Linux in pre-packaged form, ready to use. A "live distribution" is one that you can use on your computer without actually installing it. To do this, you download it and burn it to CD/DVD, or copy it to a USB drive. When you boot your PC from this CD/DVD or external drive, Linux is loaded into your PC's memory, and you can use it without having to install anything or making any changes to your existing system. You can even open, work on and close files on your hard drive.
This has limitations. Linux is likely to run more slowly than a system that has been installed on your hard drive. Live Linux distributions may be smaller and lighter to enable them to fit on a CD/DVD and to run in your PC's RAM. They should however give you a "taste" of Linux.
The thing you are most likely to notice is that Linux is different, but not very much so. Like Windows, it has a graphical interface (although it may differ quite widely in appearance, depending on the distribution you have chosen). It will provide you with different applications, but these too will be fairly familiar. LibreOffice for example, the office suite supplied with the great majority of popular Linux distributions, is very similar in appearance and operation to the pre-ribbon versions of Microsoft Office.
Which distribution to try
There are lots of different distributions to choose from. For an overview, visit Distrowatch. Distrowatch gives some indication of which distributions are currently the most popular. Browse around the information on the most popular distributions, and choose one that has a "live" version and is geared to desktop use.
If your main PC, or the one you are using to try Linux, is not particularly powerful, look for a "light" Linux distribution, i.e. one that does not make heavy demands upon your hardware.
If your first impressions of Linux inspire you to find out more, you may want to install it on your PC in order to use it more effectively. What you should probably not do, even if tempted, is try to migrate to Linux as quickly as possible. For ways of using Linux and Windows (or Windows applications) together, see Running Windows applications on Linux.