How do I create a file format for text created in my new application?

I'm just a beginner--so I really don't know the best place to post something like this. I would like to create an application that keeps track of text that I write and catalogs it. I don't want to store the information in a database--this would be something I would like to save in an individual file, like a word document or an excel file. The trouble is, I can't seem to find any information on how to do that from googling or looking in my Visual Studio books.

I'm basically working on an application for writing short stories. I want to be able to create characters, scenes and chapters, and structure them so that you can easily navigate in the tree view if you wanted to. Is there some place I could go online or a book that might point me in the right direction?