I just got a spare 250gb HDD so I was looking into putting linux on it. I've never used it, but I want to so I can know how it works. I'm looking for the best distribution so someone like myself can learn how to work it. Any suggestions?
If you just want to try it out and see/learn what you can do with it, Ubuntu.
If you want to learn Unix, I'd say Slackware or Debian. They're more hands-on, and will force you to learn how the guts of Linux work. Word of warning: you cannot be afraid of the command line.
Ubuntu is actually based on Debian. But it's more focused on presenting a simplified interface (some would say overly simplified) for Windows and Mac users.
If you're a masochist and/or want to become a Linux kernel programmer, Gentoo. You pretty much have to build it entirely from scratch, but you will learn everything about how Linux works. I cut my teeth on Unix before Linux was even around, but even I've been afraid to try Gentoo.
Or you could simply put ALL of them on your disk and boot to each one from a boot manager as your mood strikes you. Another option since there are no keys and such you could also install one and then install the others inside it with VMware.
I myself have Ubuntu with UNITY, KDE and LXDE desktops installed and I can choose the desktop for that session during sign-in.
I cut my teeth on Unix before Linux was even around, but even I've been afraid to try Debian.
You obviously haven't been watching the development of Debian over the past 20 years - it's as easy to use as Ubuntu now, nothing scary at all :-) That said I'd absolutely +1 the Ubuntu recommendation (or better still, Kubuntu or Xubuntu depending on your hardware). Also +1 to stillblue and womble about trying a bunch.
You could screw around with Arch or Gentoo (or scarier still, Linux From Scratch for real understanding) but do it in addition to the buntus or your experience will probably put you off Linux altogether. Getting Arch/Gentoo/etc up and running can feel pretty punishing.
Depends a little bit on your other hardware...but if your computer is reasonably up to date, Ubuntu is the most user friendly and easiest to pick up. If your computer is more than a few years old, you might try Puppy or LUbuntu.
I personally suggest Ubuntu because it is pretty user friendly, and it's one of the biggest if not the biggest distro out there, and it has so many tutorials. I would say they have more tutorials then any other distro. If you ever ponder about something with ubuntu google almost always has an answer. Here are the deriatives (Different desktop enviroments)
Kubuntu - Only if you have a fast computer. Very resource needy, but very elegant and pretty.
Xubuntu - A lightweight distro. A nice feature is that it has a dock.
Lubuntu - The most lightweight. Very little eyecandy.
Ubuntu - The main one, with a dock on the left side.
I think it comes down to your hardware and personal preference. Ubuntu is great for users who have decent hardware and like a little eye candy. Lubuntu is for older hardware and hits the ground running. I find Mint to be just right for my older AMD Sempron 64 with 512MB RAM. I am still new to Linux as well, and seen a video on Compiz effects, and this is why I chose to make the switch. On Ubuntu, compiz was laggy and seemed buggy. Although Mint took some configuring, Compiz runs well with my older hardware. Please note that my build has a 128MB AGP installed as well. Burn some live CDs and find which is more of your style, and note that the Distro you choose will run smoother once you do the full installation. Look at your hardware, view videos of the distro, and test drive... I found it very simple to choose a distro this way.