[st_albert]

Let me add my sincere recommendation that you read Pablo's tutorial! Not only will it give you a basic grounding in how to put together an epub, it will also be useful as a basis when you go through the WCC tutorials. Not to mention, helping you understand WHY you might want to do some of the things covered in the Sigil manual.

And since I see you are using Libre Office, I advise you to check out the "writer to latex" and "writer to epub" plugins. Don't install them as-is. They won't work on modern versions of LibreOffice or OpenOffice. But the package contains a stand-alone java program that can convert a LibreOffice .odt file to an epub (not for the faint-hearted, I admit). But if you are in any sense a coder, you will find adequate documentation in the zip file to set yourself up to convert your .odt document to an epub that has very clean code, and is easy to polish in Sigil.

Edited to add: If you take that route (writer2latex.jar), you should make sure that EVERY paragraph in your .odt file has an assigned "Paragraph Style," and every string of characters that is not ordinary (e.g. italic, or bold, or both) within a paragraph has an assigned "character style." Then make sure that every such style has an associated CSS style in the <custom>.xml configuration file. (Do not fear. The documentation should make this clear, how it works.)

Good luck!

Albert