A family of Microsoft word processing software products for creating web, email, and print documents.
If you are using an older version such as Word 2003, see http://word.mvps.org/FAQs/AppErrors/MissingMenusEtc.htm.
In Word 2010, you should be seeing Home, Insert, Page Layout, References, and some more. To see all commands of the active ribbon tab, double-click (say) Home, or right-click it and clear the check box next to Minimize the Ribbon on the context menu.