I see "->" and "<-" or "<u>" in my chapter text. What are they?

They are formatting marks written by the toolbar above the editor (version 1.9.15 and later). "<u>words</u>" underlines the words. "-> text <-" at the start and end of a paragraph centres it; "-> text" at the start alone aligns it to the right. They never appear in the exported book: PDF, EPUB, Word, Kindle and HTML show the text underlined, centred or right-aligned, and the audiobook never reads them. To remove one, click in the paragraph (or select the underlined words) and click the same toolbar icon again. You can also type these marks by hand.