You can get an idea of the Linux distros (distributions) available from distrowatch.com - feel free to try any of the op 10 listed on the right there.
They are all free. Also note that many distros offer a 'LiveCD' version - think of it as try before install.
Basically it runs directly off of the CD/DVD, so that you can see what it looks like before you decide to install it.
Of course it'll be a bit slower...
You may want to have a read of these
- this is all about the cmd line - may be very useful at times, even if you normally work at the GUI level.