Semantic authoring means to represent your personal knowlegde in a symbolic form, i.e. to write it down.
Bad news: You cannot author text content, text structure and a semantic network at the same time if you stick to your most-loved office software. You have to switch to another stack of tools. And more: You will find that you will meet a somewhat different paradigm of writing - at least compared to wysiwyg-approaches. Thus semantic authoring is much a methodology as a pure technique.
Good news: The paradigm of writing text in a structured way we suggest is a well established, basic and efficient way to represent knowledge. We heavily rely on mindmapping as the most important knowledge representation for structured writing.
In principle you can use every mindmap tool of your choice. Our tool semAuth is completely independend from the mindmap tool of your choice. However, until now we make extensive use of the format ".mm", which is supported by free and all-platform tools like freemind or - our recommendation - freeplane .