LibreOffice Writer has a built-in single-click PDF creation which I described in another video. You can download an enhancement which lets you make an EPUB file in the same way. The EPUB file has a live table of contents just like the PDF file, but the EPUB lets you change font size or rotate your phone or tablet and the excess text will reflow rather than run off the page. I have another tutorial that shows how to make headers, headings, and table of contents but also go over it in this video. You can send the EPUB file to your external device wiv Dropbox. You can bypass Caliber entirely and even read the EPUB file on your Ubuntu computer with "epub-viewer". Just right click on any EPUB file and go to Preferences and type in EPUB-VIEWER. Thereonafter, any time you click on any EPUB file it will open without Caliber. Unlike the PDF file viewer, the EPUB viewer will reflow if you change font size or width. To make ebook files other than EPUB you will have to open up Caliber. Alternately, you can download Sigil which is a full-blown ebook document editor.