What is Linux?

You might worry about having to get rid of your familiar Windows environment completely to run Linux: not so. Linux and Windows can play together nicely.
There are a couple different ways to have Windows and Linux on the same machine. You can have separate hard drives for each, or if you have only one hard drive you can partition it to be able to use both systems. If Windows is already installed you can use a repartitioning tool such as Partition Magic.
In either case, you would then use a boot loader to select which operating system you want to use each time your machine starts. Linux can use either of 2 boot loaders: LILO (Linux LOader) and GRUB (GRand Unified Boot loader).
In this dual boot scenario you can share files between both. Linux can see the Windows files, but Windows cannot see the Linux files. You can't run Windows applications in Linux, but you can use your data.

You might worry about having to get rid of your familiar Windows environment completely to run Linux: not so. Linux and Windows can play together nicely.