Suppose you're referring to this:
"Finally, with the cursor in the same spot (i.e., after the image and just before the start of the text) use the Insert -> Chapter Break command from the menu bar"
It would be more accurately stated as:
"After inserting the image, press ENTER to create a paragraph break between the image and the text. With the cursor on the right-hand side of the image use the Insert -> Chapter Break command from the menu bar (or press CTRL-ENTER)."
The reason for this is that (apparently) the chapter break is inserted at the end of the paragraph the cursor is in.