ReadUps has a browser-based reading system; you can paste in text content or upload ebooks.
If you paste in content, the less formatting it has on it the better it will look. Things pasted from Google docs will work better than Microsoft Word.
If you upload or import an ebook, it needs to be a DRM-free .epub file. You can see if an epub file is DRM-free (it doesn't have copy protection), and formatted correctly, by running it through the EPUB validator. If you get an error, the file may have problems. You can try to upload it but results will vary.
When you upload a book, you'll have access to all the chapters in a book using the table of contents pulldown in the top menu. Content scrolls vertically, but you can move between chapters by swiping left/right or clicking the arrows.
You can import a book from Feedbooks - they're usually well-formatted.
You can also bring in a webpage, using the Add URL option. We'll strip out everything but the text and serve it back to you.