In the coming month or so, I will be releasing various Open XML related code snippets. Using these snippets you easily perform simple and more complex actions with WordProcessingML, PresentationML and SpreadsheetML. Since I am moving all my Open XML related articles to OpenXMLDeveloper.org, you can find these articles on that site. The snippets tie in with the already available snippets. The overview article and first article on WordProcessingML are ready for you to read, later this week I'll also be posting items on working with paragraphs and if time permits, how to work with tables.
You can already download all WordProcessingML snippets here. The things you'll find in the MSI are a few snippets to get to the main body node, and perform various actions with paragraphs, tables and content controls. Do be aware of the fact that the snippets tie together, so if your code is missing a method, you'll probably need to use an extra snippet.
Hope it helps to get you started with Open XML!