Microsoft Word - styling

Hey All.
Problems with word - Im trying to help a friend design a long document that contains a lot of styles, bullets and numbering. The changes I make do not help and everything goes wrong.... I understand that the only thing that can help are styles. Can somebody recommend a document that may help me learn how to use styles?
Should I create a new template and copy all the document to it, or should I change all the templates in the document? What do do?