Windows 8 is the latest version of Windows. It came out in late October and you now see it on the new computers in the stores.
Windows 8 has a completely new interface to it and looks totally different than previous Windows. This is a major upgrade to Windows similar to when Windows 95 and XP were developed.
Microsoft has developed Windows 8 so that Windows looks the same on desktops, laptops, tablets, and phones. The new interface looks totally different than the old desktop (although you can get to the desktop by using the Windows button). The new interface looks like the interfaces you have already seen on mobile devices such as tablets and phones, but Windows was not a\available for these devices previously. Your different apps and applications now show on the new interface as tiles (not called icons) which are large colored areas.
Although Microsoft says Windows 8 works on all these different devices, there are actually two versions of Windows 8. There is Windows 8 RT which is for the mobile devices (tablets and phones) and it uses apps (small applications designed for mobile devices and Office 365 is available to use as online app) you get through the Windows store (similar to the iPhone getting its apps through the Apple store). This runs on devices using the ARM processor. The new Microsoft tablet called Surface runs this, but the Surface coming in January will run the other version. The other version is Windows 8 (there is an ordinary version and an enterprise version for companies) and runs on your desktops and laptops (which use processors from Intel and AMD) and the new Surface due in January and runs applications (programs as we are used to) such as Office 2010 and Photoshop, etc.
The Start menu is no longer in Windows 8, although they call the main screen the Start screen. Items like shutdown, control panel etc. are on the charms bar which appears when you go to the far right of screen and is similar to what they had as a gadgets bar in Vista.
The idea is people will see Windows the same no matter what device they use. Microsoft hopes to be the leading operating system on all devices. If you are thinking of getting Windows 8 be sure you realize the differences in the interface. Currently Microsoft is offering an upgrade to Windows 8 online for $40. Be aware that you really can only upgrade from Windows 7, but if you do move from XP or Vista it will be a new install and you will lose all your programs and settings, just not your documents.