is one of several PCB layout programs that you can get for free (other programs include KiCad and DipTrace). The free version of Eagle is somewhat limited in what it can do, DipTrace slightly more so. KiCad is open-source, and hence is completely free.
I use Eagle because its limitations are reasonable for what I need to do, and I believe that it has a better interface than KiCad.
Eagle can be downloaded here.
If you're just installing Eagle, you probably will want to use the 'Run as Freeware' licensing option when it comes up. Note that for this instructable, I'm assuming that you have Eagle 6.1 or higher installed. The files that I upload are stored in Eagle 6's xml format, and as such can't be opened by earlier versions of eagle.
First we'll cover moving around a finished project, then we'll start from scratch and design a board from start to finish.