Microsoft Windows is an operating system. It contains the instructions for your computer to open, manage, store its directories and files. The operating system also is responsible for your personalized settings (appearance, connectivity, network etc.)
Microsoft Office is a suite (collection) of commonly used applications to run on a computer - typically Excel (spreadsheet program), Word (for word processing), Access (for database creating and management), PowerPoint (for creating presentations) and Internet Explorer (web browsing). Other applications may be included.
Windows is an operating system that is characterized by what is called a "GUI", meaning "Graphical User Interface." The GUI allows you to point and click to accomplish what you want. Technically, computers don't really understand point and click, some kind of application needs to run to allow the computer to recognize what you mean, that's Windows. The name comes from the idea that a "Window" is opened and you can look at the window and see a representation of what is going on inside the computer. Windows allows you to run applications to accomplish different tasks, such as "Internet Explorer" to surf the net or even voice recognition software to replace the keyboard. Each of these would be considered to be examples of "Application software" which is independent of the operating system.
Microsoft Office is a collection of software applications, which allow you to perform different tasks. Microsoft Word allows you to generate and format documents, Microsoft Outlook allows you to send, receive and format e-mail, Microsoft Excel allows you to create spreadsheets for business or personal applications. Thes are some of the applications that are part of the "Office" collection.
Microsoft Windows is like your operating system and Microsoft Office is a series of programs like Word and Excel and many more.