A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
Murray Sargent's blog is invaluable. Start with this link: http://blogs.msdn.com/b/murrays/archive/2010/03/03/math-ribbon-entry-of-subscripts-and-superscripts.aspx and then follow the link there to the original post as well.
Or, the short answer is the _ character for subscript, and ^ for superscript.
I hope this helps.
John Guin [msft]
OneNote Test Team