Microsoft account is the new name for Windows Live ID. It is a combination of email address and password you use to sign main Microsoft services including Outlook.com, Hotmail, Messenger, and SkyDrive. A Microsoft account also gets you into other Microsoft sites such as Xbox LIVE, Zune, and Office Live.
Along with that Windows 8 introduced Microsoft account sign, Microsoft account is becoming more and more convenient. If you don't have a Microsoft account yet, read this article and follow steps below to sign up for a Microsoft account now.
P.S.: Read about how to create a Microsoft Account in Windows 8/8.1.