Noobs getting their first taste of the Linux OS tend to feel a little lost. Even though the Gnome and KDE GUIs are simple and easy to navigate, it's hard to ignore the realization that you don't really know what lurks beneath the surface of this powerful operating system. And many of those who do venture to the command prompt to do a little exploring tend to back away slowly after peeping the unfamiliar and slightly intimidating Unix-like directory structure.
Well, sink or swim, I say! There's no better way to really get to know an OS intimately than to build it yourself from the ground up. (And not all that long ago, this was just about the only way to get to know Linux at all.) Now, before ya'll get worked up, let me just say that this project should by no means be anyone's first step into the world of Linux. (Unless they have a deep yearning for adventure.) But if you've got a machine you don't mind sacrificing to your own personal edification, consider building Linux From Scratch .
LFS is an ongoing project designed to turn ordinary users into superusers. Literally. Rather than rely on others to put together a distro for you, LFS gives you all the building blocks of Linux, and a whole lot of step-by-step instructions to help you along the way. You can download LFS as a bootable Live CD loaded with everything you'll need, including the LFS book that teaches you how to install everything. From creating and mounting your partitions to installing the kernel and libraries and configuring your boot scripts, you'll build your own personalized distribution. Put in what you want. Leave out what you don't.
Once you've got your basic OS installed, you can work on building up your system to include the X GUI, security utilities, multimedia apps, and just about anything else you could want. Using BLFS (Beyond Linux From Scratch), you'll get all the instruction you need to take your install to the next level. In the end, it's a whole lot more work than installing Ubuntu, but it's a rewarding way to explore everything Linux has to offer.