You might already know that there are two different versions of Windows 8 (actually, three, but the differences between Windows 8 Pro and Windows 8 aren't huge). Those are called Windows 8 and Windows RT, and Microsoft hasn't exactly done the greatest job at informing everyone what the difference is. There's a lot of confusion out there, which is a shame, because the difference is very important and, as it turns out, not all that complicated.
Put simply, Windows 8 is for PCs, and Windows RT is for tablets. That's a slight oversimplification, but not by much. The difference lies in what is called "desktop mode." Desktop mode is basically the Windows 7 experience, largely unchanged aside from the lack of a start button and the presence of the hot corners. Hot corners are the four corners of the screen – mousing up to the upper left allows you to switch between apps and desktop mode, clicking on the lower left brings up the start screen, and either right corner brings up the Charms bar, which opens up universal search and share functions, along with settings.