What is the best way to learn Linux?Thanks!

The best way in my opinion is to play with options to see what they do, and when you find something you don’t know (how to do something, what something does, etc.) then head to Google or your favorite search engine and see what info there is about it.

If you want to try out the command line, the ‘man’ command (without the quotes) is how you look up the ‘manual’ page for other commands. for example, typing:
man ls
would show you how to use the ls command (that first letter is an L) to list what files are in a directory and
man man
would show you a bunch of options you’ll never need that you can use with the man command. A lot of commands have bunches of options you’ll never need.
to find a command related to something, try ‘apropos -s 1 ’
(the -s 1 means ‘only look for normal commands’)
such as
apropos -s 1 password
to find commands related to passwords.
(There is also second command, called ‘help’, for things that are built in to the command interpreter (shell) like ‘for’ and ‘if’ that you would mostly only use for writing a shell script.)

Other then that I think the best way to learn a system is to use it and look up what you need to. The forums that exist for Linux are a wonderful resource fairly often, because when you have a question is it likely that others before you have asked the same thing and been answered.

Check out Ubuntu. It’s Linux, free and open source.

Oh yeah, adding to what @brotherhume wrote, you can also try Ubuntu before even installing it:
Just download the “Live CD” image, burn it to a disk, and reboot with that disk in the drive so that the computer boots from the disk. You can then play around with it all you want, and if you do decide you want to install it, the icon for it is right there.

(It’s also possible to make a thumb drive that can boot to Ubuntu the same way, but I haven’t done it so I don’t know the details)

@davidgro I use the Universal USB Installer to make my bootable thumb drives.

Live CDs and “Linux on a stick” are*great* ways to try things out if for no reason other than they don’t make any changes to your computer unless you explicitly tell them to.