To create a bookmark, tap at the top of the player. If you'd like, you can add a note.
To create a highlight, play the audiobook, then tap and hold for however long you need. Here, you can add a note.
Bookmarks, notes, and highlights are saved in the audiobook under > Bookmarks (and reappear there if you borrow the book again).
In an audiobook, tap to choose between play speed options.
Or, drag down on to set a custom speed (from 0.6x-3x).