I have no idea which version of the manual page 1471 refers to, but it’s not the current one.
Either way, the text you’ve quoted comes from a section of the manual that’s called “Notation Reference”. It’s clearly the wrong place to look for instructions on how to enter a second voice, and the first Related Link under the topic is useful.
My use of the term “voices” was misinterpreted on Tuple polyrhythm alignment - #2 by pianoleo just yesterday, so clearly a description of Voices does need to be somewhere in the manual.