The familiar made better

The desktop you're used to—with its familiar folders and icons—is still here. And not just still here, it's actually better than before, with a new task manager and streamlined file management. And you can always get to your desktop—and back to your Start screen again—with a tap or click.

whole Reference from windows.microsoft.com

Programs

Use them the way you always have. Word, Excel, PowerPoint, and other programs you count on work the way you're used to. Use a mouse and keyboard and organize your stuff in folders on the desktop.

Security

Windows Defender and Windows SmartScreen can help guard your PC against viruses, spyware, and other malicious software in real time. Family Safety gives your kids some independence while still keeping tabs on them.

Mouse and keyboard

You can use a mouse and keyboard to work on your Windows desktop the way you always have. And things you do with touch, like using apps from the Windows Store and getting around on your Start screen, can also be done with a mouse and keyboard.

Search once, go anywhere

Bing smart search gives you results from your PC, your apps, and the web. Results are in a clean, graphic view so you can quickly get to what you're looking for. (Certain features unavailable in some regions.)

See more, do more

Windows 8.1 lets you work the way you want, and flow smoothly from one thing to another. Pull up a Wikipedia article during a chat with a friend to settle a debate. Play a music video while polishing your resume. Depending on the size of your screen, you can see up to four apps at once.

Your Windows, everywhere

It goes where you go.

Use your Microsoft account to sign in to any of your devices running Windows 8.1, and you'll see the same layout, apps, and settings. Signing in with your Microsoft Account (which is simply an email address and password of your choice) also gives you access to a world of apps from the Windows Store, and lets you save, view, and edit your documents and photos online with SkyDrive.

SkyDrive

Your files are always with you

SkyDrive is free online storage that's built into Windows 8.1. Save documents, photos, and other files to SkyDrive automatically, and get to them anytime, from any of your PCs or devices. And you can use SkyDrive to protect your files if something happens to your PC.

You can also use SkyDrive to share and collaborate with others, and see your stuff on mobile and non-Windows devices.

Internet Explorer 11

Fast, fluid, built for touch

Internet Explorer 11 is built for touch—now with larger tabs, simpler controls, and fluid response to gestures. Internet Explorer harnesses the power of hardware acceleration, so sites load faster and browsing’s smoother.

Skype

Video, voice, and instant messaging

The always-on app that makes staying in touch with all your contacts easier than ever. Keep in touch with video and voice calls and instant messaging, all from one app. Call any phone quickly and easily. All Skype-to-Skype video and voice calls are free, and your messages are delivered straight to you no matter what you're doing. Snap Skype left or right and do more while you IM, video call, or keep an eye on your home screen.

Windows Store

Load up on apps

Open the Windows Store right from your Start screen to browse and download apps for cooking, photos, sports, news, and a lot more—many of them free. Sort by price, rating, and category. Find old favorites and hot new apps.